Nice attention to colour there. My daughter made me recolour her character too, it makes a difference.
I'm generally a core books DM, but if a player brought a cool concept like the stuff we're seeing here, I'd allow it.
Yep. Doing a color and tweaking the pose makes a big difference.
The prebuild "themes" are a great place to start with colours, but a second pass is very very worthwhile. For example, I swapped the shell color on the tiefling to make it pop a bit more, made her chest-strap black, tweaked a few other things to make it all match up.
For the cleric, I did a pass to make things strategically black/grey to make it raven-queen esque on top of the base green (which reflects the fact she is a yaun-ti).
Weapons don't get very colored, so I find myself redoing them alot, especially if the PC has magical ones. The cat-person has a sunblade (I took a crystal sword and used a glowing yellow and orange), and a flame blade (volcanic rock blade with a medium flame effect).
Try to tie the colors used on the weapon back to the character as well. The battle-gnome's sword and slightly blue-tinged hair and blue eyes hook up a bit. And on the tiefling, I modified some of the otherwise white bits to match some of the colors used for her necrotic-acid blades.
The "bulby" and "ice" magic effects I find I don't like as much as the lighting and fire. But you can do a lot with fun colors on fire.
The "soften" feature on faces isn't much, but it can make a character look right or not. Cat-faces, for example, look way to lion-like; the above has "max soften" to make it feel more like a cat.
Advanced poses are needed to get a good screenshot. Twisting wrists to position shields and weapons right, heads to align (or not) with the camera, eyes locked on (or not). Moving weapons to hide or show parts of the rest of the figure.
The "blend" is a poorly named feature. I haven't used it for blending, I use it to find the model's current palette; so I can copy the leather used on the belt to the grip of the sword, for example.
Having some willingness to do character design (or compromise) is good. You won't be able to faithfully recreate a drawing or sketch, but you can extract elements out of that sketch (or other details) to generate a look that conveys similar stuff about the character. You have a limited palette of body pieces, positions, gear and expressions.
So the "staff of striking" got a huge green crystal head on its end. That probably wasn't what it would be imagined as outside of this drawing, but it does evoke somewhat of the right feeling.
Similarly for the staff of thunder and lightning. I used the crystal look because I could make it seem as if the staff itself had electricity going through it. There was no plan prior to messing with this about what the staff was made of, or what it looked like.
