Why has my old glads turned yellow in color? I had all colors but now I have mostly yellow flowers. Why?
Glads Turned Yellow in Color
Certified GKH Gardening Expert
There are a number of reasons for this odd occurrence: grafted plants can revert back to their rootstock, stress from transplanting or being left in ground too long (bulbs), seedlings which produce differently than parent, age of plant (likely the case with yours) can cause faded flowers or yellow/white blooms, soil pH, and mutations.
Here is more information: https://www.gardeningknowhow.com/plant-problems/environmental/fixing-color-faded-flowers.htm