Have you used any reference for the image so far? If so, providing it could help everyone who wants to say something a lot.

they look cute.
I wouldn't think of them as mecha, rather in a cuddly, funny way.
You use a ot of round forms and to few sharp angles to make them appear threatening, like most mechas should be.

Designwise maybe not what you wanted, but still totally adorable.

I'd say you take them a step further, by making sure that your forms appear solid and you take light for your shading in consideration.


The forum also has a zoom-function
leftclick on an image zooms in
ctrl+leftclick zooms out.
Pixel-perfectly.

Usually it's pretty easy to tell someone "do some hue shift" to get more alive colors in a piece which is otherwise death.
The problem with those pieces is that there is not much artistic craftmanship in them, that a "shortcut" help like "hue-shift" truly helps.
Hue shifting is a simplified term for something which goes on with color, but is much more complicated.

The problem you run into with your palettebuildig is that you assumed approximately the same values for each ramp of colors.
Another problem you have going on is that all your darkest shades and all your brightest shades are looking in avg. the same,
all first shades seem to have the same saturation, same goes for all second shades as a group and so forth.

THe result of those flaws is that the only usable colors in your palette as it is, are currently the midtones.

You run in trouble with red and yellow, because they work only at specific hue and different value and saturation levels.

also the saturation levels some colors look "best" or "truest" at vary a lot. Red only looks like red in the really high saturated area.
While blue and green work really nice in mid-saturated levels.
And some grays only will work with really little saturation.

maybe this image helps to make my points clearer:


for example:
yellow seems to look best with high value, high saturation and gets "muddy" really quick in the lower levels.
blue seems to look best in mid value high saturation but there are a lot of beautiful over a much wider bightness and saturation field.

Just throw any mathematics for this topic over board and don't try to come up with the same values for each colortype.
It won't work because reality doesn't work that way.

Learn a bunch of colors you like and where the are in the colorcycle.
https://en.wikipedia.org/wiki/List_of_colors:_A%E2%80%93F

for example if you look for "sand" what you will get will be at the level it usually should be.

Once you know some colors and where the are, it gets easier to learn new colors and remember where they are in the color-spectrum.
And then it gets much easier to understand why the color you want to achieve can't be achieved with the model you used for your current palettebuilding.

tried to fix up some of the lighting
put in reflections and him and on the metal parts - complimentary to the lightsource
tried to smoothen out the shine and increase the contrast to make them seem more powerfull

turned him a bit more sidewards
added a bit of perspective, by moving the front shoulder up and the rear shoulder down

also adjusted the pose a bit

I don't think the drills are connected in a realistic way with the arm and I don't think that metal underwear like this would work. But those are just observations, i didn't change any of it to keep it true to your concept.

will be going there business related.