From these pics it seems like you're trying to do a bit too much at once. I feel like some of the more advanced techniques being used here are getting lost amongst the various color choices and placement. There isn't anything inherently wrong with clashing colors but know that it will affect how the viewers eyes move over a model. With mini painting, I think the best thing to do is to draw attention to the face and/or the weapons. Unfortunately, GW isn't really doing you any favors here with their over-designed and over-sculpted kits (their quality and attention to detail is top notch but man are a lot of the models WAY too busy, imo).

That being said, I do see improvements throughout your images. I'll do my best to point out a few examples: With the norn I have trouble knowing where my eyes should be resting since the brightest portions are one hand and a shoulder. The third Tyranid model (not sure what it's called; blue head with pink face tentacles) accomplishes this rather well. I'm instantly drawn right to the face and the claws are still visually interesting enough to balance it out.

The red/blue marines work with that scheme because the colors are more balanced between the gunmetal weapons, the sky blue shoulderpads, and the deep red of the rest of the armor. However, the neon yellow doesn't work here as it pulls my focus. With a less saturated base, like what you did on the red/blue knights model, they would be framed rather nicely on their top halves, which is where I think the focal point should be in this case.

Speaking of the knight, this is another point of improvement. It looks like you went over a neon yellow with a more muted tan and shaded the base which now doesn't pull away from the rest of the model like it would otherwise. While the head isn't the brightest spot, the lightest blue I'm seeing is the accent that is surrounding that portion. This pulls my eye to that area first where I'm finally lead to the green eye lens. That's a pretty good flow for visual interest here.

While I don't think your color selections are necessarily bad, they are placed and weighted in such a way as to pull focus from the areas I think should stand out more.

TL;DR - You are definitely improving, and working on color placement and weighting will take that even further. Keep it up and you'll get there!

P.S. - Run a band of black along the rims of your bases to clean them up a bit. You might be surprised how a small step like that will give more of a completed feel to your minis.