Partially Dying/Streaking Synthetic Wigs?

I found a wig that would work great for a custom of my fave synth, CiFlower. However, I'm not too sure how to add her signature purple "stripes" of hair. 

I've had a look online and seen mixed info on whether synthetic fibres can even be dyed or not, so I was wondering what my options would be in this case. 

You can sew some purple hair tracks on the top. Then use some of the original hair to hide the tracks. As for the gradient I'm not sure.

If the wig is heat resistant you can dye it with synthetic fabric dye like Rit DyeMore. It has to be heat resistant because you have to boil it for the dye to work. Idk if the dyed wig would stain the vinyl. The gradient is pretty light so it might be ok.

iDye Poly is a pretty good option to dye synthetic wigs! I think for the gradient that would definitely be a good option.

For the purple streaks I second the opinion that it would be easiest to sew in some wefts.