I've a number of different skillsets under my belt, and they overlap in strange and wonderful ways. I work as a background artist, illustrator and comic colourist. From a layman's perspective, they could come off as being more or less the same thing.
I'm back colouring comics for the first time in a while, and as always, the first page is always painful to work through. Firstly, it's the only job I do where I'm not technically drawing anything. Everything else allows building, adding, fixing.
Colouring has you in a purely supportive role; what has been done before you is set in stone and that is what you work with. I've worked with artists of many different skill levels and you can see in the great ones how much time and consideration has been put into the visual weight of each element. Even doing colour holds upsets that balance, and you are literally messing with their storytelling.
Over a longer run, a rapport and understanding can be built in an art team, and you can tell where you can push the envelope or where to play it safe. Page 1 though, it's still too soon to know, so it's safe all the way.
Technically, there's different tricks to flatting and colouring other people's lines and this takes a while to get used to, and learning how to compliment each artist's visual language.
It's not uncommon for me to colour a first page two or three times, just so I get used to the lines, the tone of the story and what is feasible to get done under deadline. Putting in that work early on will save you from going over the top and overburdening yourself later on.
For some of the more novice art teams, the penciller is still getting used to the story as well, so page one will usually host a lot of superfluous traits that may be honed as the book progresses. Things like how clean the lineart is, resolutions, borders and so on are for a lot of people mistakes yet to be made and usually will only be made once. So teams grow, and get better, and great books get made.
There are some small things that make life incredibly awkward for people further down the chain This is why I recommend that anyone wanting to work in any creative collaborative field should try AS MANY of the different disciplines in their field as possible. Harper Lee said it best
"You never really understand a person until you consider things from his point of view . . . until you climb into his skin and walk around in it."
I've immense respect for everyone in every part of the comics machine, and I do my best to give as much leeway as possible in any project I work on. After all, it is a process, sometimes clunky at first but can become a great adventure that lets you do cool and different things. Already, three pages in today it's like the gears have been greased and I'm back having fun.
Speaking of which, it's time to get back to work :D