Why doesn't Captain Janeway initiate Blue Alert in the episode "Dragon's Teeth"? Note that the threat from the Turei had ended before she gave the order to land the ship. (Netflix time index: 6:20)
Even though the imminent threat from the Turei had passed, Voyager was still at red alert status when landing on the planet.
There is no purple (combination of red and blue) alert status; it has to be one or the other and Captain Janeway decided to remain at the higher red alert ship status instead of cancelling it and initiating a whole new blue alert emergency protocol.
On a vessel with landing capabilities, such as the Intrepid-class, blue alert was called as an indication that the ship was preparing either to land or to take off; the crew would then need to report to code blue stations, in order to aid in the landing/liftoff procedures. (VOY: "The 37's", "Demon") Blue alert was the minimum required ship status for landing an Intrepid-class starship, as the USS Voyager did make a landing while at red alert without switching to blue alert status. (VOY: "Dragon's Teeth")
source: Memory Alpha - Blue Alert
Different ship statuses (red alert, yellow alert, blue alert, etc) have different protocols to follow. It's wiser to keep your crew at red alert ship status than cancel the red alert and immediately initiate a blue alert. Blue alert was only the minimum ship status for a landing; there is nothing prohibiting a higher state of readiness.