Disclaimer: For the unlikely case that any of the owners of the OCs are going to see this post: I chose your OCs as examples because they where the first that came to mind. This is not a critique to any of you as a person or for what you do in the community, I am simply my personal judgement over how your characters look from an artist’s perspective and nothing more. All of the following solely based on my personal opinion and taste.
@PacificGreen
Well, I said
most OCs featured in that animation, not all of them.
Though one could argue that using absolute black as the mane/tail colour is a bad design choice when speaking of the MLP art style, but it works with his own style, so you got that.
What I am mainly referring to is the overabundance of red eyes, too strongly saturated colours and unharmonic colour palettes. As a positive example I would like to bring up DigiBrony’s ponysona:
The colours harmonize well with each other, you can tell that the coat isn’t simply grey but a desaturated purple, the hairstyle is unique and yet toned down and the cutie mark, while featuring a lot of different colours, doesn’t pop to strongly. The design isn’t perfect, but it’s definitely one of the better ones out there. If I had to tweak it, I would maybe change the eyecolour to violet or yellow and rework the details on the CM (remove the outlines, redraw the magnifying glass, etc.)
If you would put him into the show, he would fit in just nicely.
On the other hand you got IloveKimPossibleAlot:
This design is just all over the place. None of the colour harmonize, the contrast between the eyes and the coat is almost indistinguishable, the colours are to strongly saturated and the cutie mark pops too strongly.
The way to fix this is a bit too complicated to explain, so have a quick altered version:
This is of course not perfect, but better than the original, imo.
I hope you can get an idea of what I mean here.
Of course having saturated colours isn’t a bad design choice per se, but in the context of MLP it is, since the entire show’s aesthetics is based on pastel colours. In order to design a fitting OC one must uderstand how the other official characters where designed. The best test to see if your design is good (= fitting for the MLP show style), is by putting your oc next to a bunch of official characters and if yours pops out too strongly, you should probably tweak it until it doesn’t anymore.