It sounds like the most vigorous colors are growing at the expense of the weaker ones. It's probable that the reds rotted, and only the lighter colors are surviving. The corms themselves do not change color.

It must be truly spectacular in your garden when they bloom.

Renee

All of my glads return an orange color, regardless of what color they were. Al

I didn't realize there could be such a difference in vigor.
A pastel yellow, established in a garden new to me, would not be eradicated! Each corm produced 30-50 babies! Unreal. No wonder I couldn't eliminate it until the top 6 inches of soil was removed.

I planted Wine & Roses --- few babies but very reliable. I have also had others and they remain true. One very special color did die out. A neighbor has a great amethyst purple I've admired for 8 years+. No other color and it has only doubled - slow increaser.