I like how these MOCs look! They're pleasingly simple and fun to look at. But there are some aspects of the MOCs that are rather off-putting...
Arkko: The white and the keetorange are fairly well spread out, especially so on the arms. But the white is predominate on the legs where I think that there should be some more keetorange. Also, Arkko's mask and the blue pins break the color scheme, where his main colors are black, white, and keetorange, his mask is yellow and the pins holding the bohrok eyes in are blue.
Jehka: Probably my favorite out of the bunch. I like the torso design and how it flows with the color scheme of the MOC. But I feel that the grey looks somewhat out-of-place on Jehka, where I personally think silver would look better.
Desula: The colors are nice and balanced here for the most part between the old gold, metru blue, and keetorange. But the mata blue looks too bright on Desula's chest. The mata blue on the weapon is good, but I would recommend swapping the keetorange shield piece out for a silver one.
Belhiru: The variants of brown on his arms look rather odd. It goes from brown to light brown. The throwbot feet on his chest are also black, where almost no black exists on the rest of the MOC, you see a lot of it on Belhiru's chest where, in my opinion, there should be brown.
Ralis: The color scheme is broken here. For example, on the arms, you have keetorange on black, and on the legs you have black on keetorange. The weapons look very nice and the use of the metru armor is very clever.
These are your MOCs and it's up to you whether they're finished or not, I'm just offering up my suggestions. ^^