Happening to me too, really annoying as I was planning to build quite a bit today in Studio.
Update: I found a simple solution to this problem! After selecting the colour value you want for a part in the menu, click okay, and then change the colour of the part again. After clicking away it’ll revert to the colour you originally picked.
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I would also like to report this issue as well.
In Roblox Studio, each time I change the color of a TextLabel and then select something else, the color switches back.
It seems that the only work around that exists is to copy and paste the RGB value into the color property, avoiding the use of the color picker to input it in for you.
Sorry for the inconvenience. The change was reverted earlier this morning. Please restart Studio and you should no longer experience this bug.