While my heart belongs to the fossil dragonite, as a wildcard, let me vouch for the Wigglytuff from Vending Series 1. It instantly made an otherwise neutral-to-me pokemon appealing. The background is sort of smokey and mysterious at either dawn or dusk, and wigglytuff singing peacefully in the foreground is just really nice.
Theater VS Pack Alto Mare’s Latios, wish I could put the Latias here too as they really are beautiful as a pair, but the Latios barely wins out of the two for me.
My number one pick was pretty obvious for this Type, since it’s my second favorite TCG card in general:
Will pick and post some other amazing Colorless-Type cards in a moment. 
Greetz,
Quuador
Some of my other favorites in no particular order:
Both Bouffalant and Doduo are of course part of a connected story:
I love the happy ending for the two little Natu in the snow, now warm on top of Bouffalant. And although both Doduo are amazing, I’ve only mentioned the second because the truck has the first artwork as logo as well. And I kinda like the durpy look of Doduo sitting like that. 
Enjoying the sun and a well-deserved rest.
Teddiursa and Ursaring have a lot of amazing artworks tbh, but I like these two the most. Both very cute, and additional humans/Pokémon in the artwork are always a bonus for me.
This Lugia full art is likely based on the Shining Gyarados, whom I’ve posted before in the Positive Energy Water thread. A very awesome looking artwork in the unique illustrator kawayoo art-style.
And the Noctowl is more an honorable mention. There are some other Colorless artworks I like slightly more, but nonetheless this is probably one of my favorite Ken Sugimori artworks, and probably my favorite that uses a generic background. Ken Sugimori artworks are of course known for their stock images, with random backgrounds, often using blurred irl photos. Most of them are therefore rather boring and uninspiring, which is why I like this one so much, since the editor did some effort of adding two smaller Noctowl in the back, making them smaller, mirroring one of them, and making their eyes glow. Typing it out like that, it may not seem much, but it makes the artwork so much better than so many other Ken Sugimori artworks.
And tbh, nighty backgrounds almost always look great, so that is likely an additional factor of why I like this artwork in particular so much. 
Greetz,
Quuador
Amazed no one posted the waku waku Everyone’s Exciting Battles box Tangela!
I’m a moron, and didn’t read the thread title again…
This thread is for colorless, and tangela is leaf… obviously…
Today, my boss sent me home after my first session. Said I looked tired. 
Clearly, I was.
Salamence (ex dragon)
I’ve always thought that Arita’s depiction of Salamence here is really cool, maintaining his intimidating presence in a rarely seen top-down view.
While not one of my favorite arita illus., I also love the uniqueness of this card! It always stood out to me within the body of Arita’s work.
