Coroutines are not appropriate for fading in and out. They just aren’t, even if 99% of tutorials use them. It’s a horribly complicated way to do something that us ultra super simple.
Fading, simple and easy:
If you insist on sticking with the above code, are you sure you’re not getting errors about initializing colors with negative numbers??
Make sure your log console selector buttons are enabled. See this graphic:
The other thing is you are relying on the color channels to precisely store your change over time.
I don’t think there’s any guarantee if you put an arbitrary float point value into a color channel that the same float point value would come back. For instance, colors may be internally stored as RGBA with only 8 bits of info per channel.
Instead, keep your own floats and adjust and check them, then set the colors directly.