Of course, you can get wigs to pull off the crazy colours but don't forget your eyebrows too! Here's sharing a small tip to save a few bucks. Instead of buying crazy coloured eye pencil which you'll only use a few times, you can rely on eyeshadows instead! Most of us probably already have a palette of eyeshadow with a dozens of colours but all you ever use is brown.
Now is a good time to use up the rest of the colors by using them as a eyebrow colour. The key to making this eyeshadow method work is to first get a good base and finding ways to make the eyeshadow stick onto the brows.
There are professional products one can get to cover over eyebrows entirely. But I usually just use a fairly thick amount of concealer to dab over my brows and call it done =X. After that, use a sponge applicator or angled brush to dab eyeshadow on. I believe cotton swabs could do the work too but I've never tried it myself.
Usually the concealer would stick the eyeshadow well enough. But if it doesn't, you could try applying a bit of vaseline or lip balm. Or you can wet the brush/sponge/cotton swab before you pick up the eyeshadow to get a more concentrated colour. Other than eyeshadow, the same can be used with your Blusher and Lipsticks. Seriously, I've tried it xD.
In fact, this is what I do for my Megurine Luka, Shakugan no Shana , Kagamine Rin, Himura Kenshin and Mogami Kyoko cosplays.
I have naturally thick and well angled eyebrows *grins* so just layering colours on this way works very well for me. As a disclaimer, I prefer to look 'natural' and 'adolescent' (as required by the characters I cosplay) so no plucked and overly angled eyebrows for me. Which is just as well.
I've never really had thin eyebrows so I don't know how this method would turn out for thin brows. Let me know how it works for you =)!