When did you get the game?
I have to say I got it from Early Access day, the 19 and do not experience this issue.
I do hate that I can't colour certain things though but that's another story.
I also want to urge you to:
Please use the search function before posting a new question and upvote existing ones to bring more attention to them, It will help us a lot. <3
...for your question, I'm pretty certain, was asked on Mar 11 in Bug Report by BTSSB123
https://questions.satisfactorygame.com/3896/colored-buildings-being-reset-after-painting-new-buildings
Let's collaborate, think community and play nice m'kay.
Cheers