Q.I thought I purchased a pinkish purple pluming pampas and after 3 years it is finally blooming with white plumes. Will they chang
e color or can I change color with fertilizer ( like a hydrangea?)

Certified GKH Gardening Expert
Unfortunately, true pampas grass will only slightly darken from the standard blooming variety, and with very little color change. There are other grasses that are marketed as pampas grass, but are really another species. They will change many colors depending on the cultivar that you choose. There will be no real way to change the color of your grass, unfortunately.
This article will give you more information on the care of these: https://www.gardeningknowhow.com/ornamental/foliage/pampas-grass/growing-pampas-grass.htm