I wonder if you're thinking of the short story Plum Pie. Zombie Green. Yellow Bee. Purple Monster. from Jen Campbell's recent anthology The Beginning of the World in the Middle of the Night.

In the story the colour codes are used to send secret messages:

At the next petrol station, I find a stamp crumpled at the bottom of my rucksack. We all scribble a letter on an empty packet of tulip seeds and address it to Lily’s favourite newspaper. We want to place an advert, in the hope that she might see it. We argue over what it should say. I want to send her a secret message in HTML colour codes. #7D0541 #CFECEC, which means ‘Bullet Shell’ and ‘Pale Blue Lily’, to let her know that we are fighting and we hope she’s fighting, too.

I wonder if you're thinking of the short story Plum Pie. Zombie Green. Yellow Bee. Purple Monster. from Jen Campbell's recent anthology The Beginning of the World in the Middle of the Night.

In the story the colour codes are used to send secret messages:

At the next petrol station, I find a stamp crumpled at the bottom of my rucksack. We all scribble a letter on an empty packet of tulip seeds and address it to Lily’s favourite newspaper. We want to place an advert, in the hope that she might see it. We argue over what it should say. I want to send her a secret message in HTML colour codes. #7D0541 #CFECEC, which means ‘Bullet Shell’ and ‘Pale Blue Lily’, to let her know that we are fighting and we hope she’s fighting, too.