Not sure which my logo versions your're refering to as the "4th". Is it the bottom right version on dark background?

(can you point that out on my image please).

I like purple will work on a purple version.

With regard to the ostrich I think it might be hard to achive a simplify version that could be used as a logo/icon, I'm trying to visualize how it would work in small sizes like the 96x96px app icon