Codes make a 10x10 picture - Theory
The fact that the all the codes so far add up to 10 and are color coded, I think you can lay these out on a 10x10 grid (since there are 10 days) and using the colors of the numbers as the colors or the picture, possibly make a picture that means something. See what I started below, I'll keep it updated as I see the rest of the codes when they get posted to see what it makes.
EDIT: Color code for day 3 line was updated to be 1B-1R-2G-2R-2G-1R-1B per /u/Blakvomit
EDIT2: As more people get day three, I see more comments that the green looks like grey. I'm going to leave the color as green for the moment just to represent the third color since everyone is in agreement that there is the color black, red and a third that's neither. I'm thinking if this ends up being a picture, we'll still be able to tell what it is regardless if I use grey or green As I see more pictures I'm convinced the color is grey (I think they may intend for the color to be white, but since you can't print white, they picked grey), either way the color has been updated to be grey.
EDIT3: Color Code for day 4 was added to updated 1B-2Blue-1G-2R-2Blue-1G-1R per /u/aequitus
EDIT4: I'm adding descriptors of the envelope colors to what we are guessing the days are since only Day 1 and 2 are identified in the contents and 3 and 4 are just assumptions.
EDIT5: Color code for day 5 added as supplied by /u/krakmunky69. 1R-2Blue-1G-2R-2Blue-1G-1R
EDIT6: Color code for day 6 added as supplied by /u/mservy. 2R-1G-4R-1G-2R
EDIT7: Color code for day 7 added as supplied by /u/Gbutera. 10R
EDIT8: Color code for day 8 added as supplied by /u/SDMusic. 10R
EDIT9: Color code for day 9 added as supplied by /u/TCMassacre. 1R-1B-2R-2B-2R-1B-1R
EDIT10: Color code for day 10 added as supplied by /u/JSchell927. 1R-2B-1R-2B-1R-2B-1R