The hair spikes shapes are looking good, the spikiness reads well! I'd work on redrawing one half so that it's not mirrored though. Perfect symmetry looks unnatural for hair.
The back view also seems lighter than all the others, you're using your darker shadows there much less. Work some of those shadows in there.
You have a decent sense of form, with the spikes at the back of his head being in shadow. Depending on the lighting you want, you could benefit from extending that shadow upwards a little.
The spikes on the forehead should probably cast a shadow. Just switching the highlights on the forehead to the skin shadow colour should do it.
The palette isn't unattractive, but there are two potential issues:
1. Real blonde hair, even dyed blonde hair, isn't yellow. If you're looking to make blonde, your colours are all wrong, and looking at reference should help you find the colours you want. If you are going for outright yellow hair instead of blonde hair, then you're on the right track.
2. The orange shadows might be a bit too saturated. I'd darken and slightly desaturate the shadow colour.
I don't think you need that lightest highlight colour. It doesn't read at 1x, and hair spikes aren't smooth enough to have distinct highlights like that, so highlights make them look plastic.
Here is an edit incorporating some of the above suggestions:
The version on the left has the highlights removed, shadow desaturated a little, and with a shadow cast on the forehead. The version on the right has slightly more realistic blonde hair, in case that's what you want. Real blonde hair isn't really yellow, it more tan-coloured.
