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Throughout the Star Wars saga, no matter the era, no matter who's broadcasting, blue holograms are exceedingly common.

Hologram image 1 Hologram image 2 Hologram image 3 Hologram image 4

Additionally, Snoke's hologram occasionally flashes blue.

Hologram image 8

However, multi- and full-color holograms do exist.

Hologram image 5 Hologram image 6

If these more advanced holograms exist, why aren't they more commonly used? And what exactly makes the holograms blue in the first place?

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    Leia's hologram is actually in color, but with a bluish tint (you can see it's in color when her face is visible), and so was the pre-special edition version of Palpatine's ESB hologram. In fact, color holograms seem to be the norm in the Original Trilogy. – Thunderforge Mar 6 '16 at 22:36
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    Entirely speculative (so not an answer), but blue light has a very short wavelength. Perhaps there's some pseudo-scientific explanation that could be retconned around compression and transmission of holographic imagery as an in-universe explanation. – Jane S Mar 7 '16 at 3:14
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    @Jane S: Blue light has the potential to be sharper and crisper than red or green parts of the spectrum, especially if you have a tiny emitter projecting to a huge image. Although my guess is it's more along the lines of making it clear to the Earth viewer it's a hologram, rather than being an in-universe, canon representation of all holographic imagery. – MichaelS Mar 7 '16 at 6:47
  • @MichaelS Oh, I have no doubt as to the out of universe reason. But I was trying to offer an in universe reason :) – Jane S Mar 7 '16 at 8:07
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    Was the first color hologram transmitted over a great distance? The 2nd color hologram was probably generated by a computer within the room or nearby. All the 'blue tinge' holograms seen, were presumably broadcast interstellar distances, or in the case of R2s message from Leia, stored on (what might be) limited memory. In those cases, the bandwidth required/size of the message would logically have called for less color bands and less 'bits' than those generated by nearby machines on the fly, or broadcast only over short distances. – Andrew Thompson Mar 7 '16 at 8:08
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If you look at holograms during the Clone Wars and even during the Empire period, the image feed frequently receives static. This suggests the possibility that hologram technology isn't perfected yet, or at least the good ones are near-prohibitively expensive. Hologram technology may still be in the same phase of their history as when we were transiting from b/w to colour television in real life.

Edit: As brought up in the comments, the Wookiepedia article on holograms describe the technological progression over time in both canon and Legends, at least discussed to a degree adequate for this question.

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    Surely Chancellor Palpetine and Darth Vader could afford higher quality hologram? – Rogue Jedi Mar 7 '16 at 3:17
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    @RogueJedi - The static helps hides Palpatine's wrinkles, and the blurry, staticy image just makes Vader seem even more terrifying when he is there in person. – Rex Kerr Mar 7 '16 at 4:18
  • This Star Wars wikia page says color holograms were in place near the end of the Clone Wars in high-end locations, such as a virtual zoo for extinct animals. If holograms are fairly new in the prequel movies, then the Empire's takeover stunted the tech growth, it would make sense that they remained about the same quality throughout the original trilogy, especially for mass-produced, handheld projectors. – MichaelS Mar 7 '16 at 11:04
  • Red holograms did exist prior to the start of the Clone Wars, see this image from AotC...and red holograms were also seen on The Clone Wars series, as in this image (though I only seem to recall bad guys using them, maybe it was a separatist-specific technology at the time?) – Hypnosifl Mar 10 '16 at 2:15
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    Probably not a good guy bad guy thing...during Ep 1 the Trade Federation used blue. Probably just technical reasons one particular variant is preferred over another. Like how Imperials shoot green bolts and Rebels shoot red bolts. – thegreatjedi Mar 10 '16 at 3:35
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You don't really have light sources which are all that broad spectrum- each is associated with a particular temperature dictated by the technology. The technology of holograms remains one of light projection, and blue light is clearly the color associated with the illuminator associated with that technology.

Taking this a little further, given that there are other colors besides blue, The blue light is acting as a sort of carrier wave- it illuminates dust particles in the air to see the image, creating the "screen". Other colors can be projected on to the illuminated area which give contrast, but it is the blue light which is the workhorse and will bleed through.

In instances where non-blue tints holograms are present, they may be in special setups. Examples can include: pre-rendered CGI creations broadcast in a specialty projection area. I don't believe we have ever seen live broadcast which was not blue (which would seem to hint that it requires a fair amount of computational horsepower to overcome). But what about Leia's message? Well, it was the equivalent of recorded in a rush in a prison from a hand-held camcorder. Works well enough for the purpose but you wouldn't expect anything Spielburgian.

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You can explain the blue tint with Rayleigh Scattering. Rayleigh scattering occurs when molecules and fine particles in the air absorb some wavelengths and reflect others. Shorter (blue) wavelengths from the holographic projector are scattered more easily than longer (red) wavelengths, so when that light hits fine particles and molecules, the blue light scatters and we see that. Red and yellow sunlight is absorbed, so we don't see that.

That's the same answer for "Why is the sky blue?"

There are several examples where George Lucas famously got the physics wrong. (e.g. - This is the ship that made the Kessel run in 12 parsecs. A parsec is a measurement of length, not time.) This is one case where Lucas inadvertently chose the right color and the physics would back him up.

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