Dying Mature White Hair Pastel Colors

None of the semi permanent colors sold at Sally Beauty (Manic Panic, Arctic Fox, Jazzing) will take on my very fine white hairs. The hair that hasn't lost pigment is very dark brown, almost black, and fine and wavy. The whites are actually transparent. I've tried processing with heat, but nothing. I had better luck with crazy colors in the 80s and 90s. And I know Splat exists, but it just looks tacky to me.

I'm old(er) and stuck in Amerikkka, and wish to satisfy a few harmless whims while I still can and dye the white streaks either seafoam green or lilac. Hope someone with skills and time can help me out. Thanks for reading.