Hello thar, Luve :3
I find the sketches you've done are beautiful and look highly realistic to me! I like the compositions of all three and think they work really well, especially the panda.
As for coloring, it's true that brown paper has a tendency to soak up watercolor. But there's no reason to do any differently what you already do now. Treat the watercolor work like an under painting, and then go in and bring it up further (brighter) with an opaque paint like acrylic ink, acrylic, or oil. Or digitally, if you like digital.
Color-wise I'm not the greatest, so I'm afraid to give an opinion about that, but I wanted to say I love your sketches! I love how they look realistic yet very "you", if you know what I mean. :)
Your sketches are wonderful. :)
As for coloring, I don't think there is any problem with the brown paper and I like either of your styles- brush pen or watercolor. I like Hibbary's suggestion - you can always up the saturation either digitally or with acrylics or even watercolor if you're using the tube type.
You do really well in the more subdued color tones but with the brights, I think it's just a matter of pulling out the bright reds/lighting in the panda and maybe with bright green in the background, golden/yellow lighting, and the same in the tamarin - contrasty green and gold. I was tempted to move these cards into the neutral tones but then you wouldn't be able to do the green in the forest - the bamboo, leaves, etc, and both of these critters lend themselves to a bright color palette really well. :)
I wouldn't worry about the inconsistency of the media - all of the cards are utilizing different methods and styles from super realistic to quite stylized and your style shines through in whatever media you choose. :)
did some fiddling in photoshop and i do like the idea of the usual brown paper coloring with the saturation beefed up digitally! thank you!!
So Cute!!! I think both coloring styles would work and perhaps you could do half one way and half the other. ;)I would do the cool tones on the normal paper and the brights on the color paper. You can always tweek it a bit with the contrast in photoshop if they do not stand out as much as you like.