The way partial doors would work is that if you don't have enough keys for a partial door, you would still be able to open the door partially. As an example, if you had two blue keys and a partial blue door that requires 4 keys and you try to open it, all your blue keys  get removed, and the key requirement of that door gets decreased by the number of keys you had. So in this case the key requirement would change from 4 to 4 - 2 = 2. Now, this may seem equivalent to just having multiple one key doors in a row, but there are a few key (heh) differences. First of all, you would be able to open a partial door with just one master key. Second of all, you can make partial doors have high key requirements which otherwise would require A LOT of one key doors. Third, if  you don't have enough, it acts like a blast door with it using  all your keys. (the rest is spoilers, use rot13 to decode) Nyfb, guvf qbbe jbhyq unir vagrerfgvat vzcyvpngvbaf jvgu artngvir znfgre xrlf, nf V'z abg fher ubj gur qbbe jbhyq jbex jvgu gubfr. Creuncf jura gur qbbe vf bcrarq naq erohvyg, gur erohvyg qbbe jbhyq unir gur xrl erdhverzrag gur qbbe unq orsber lbh bcrarq vg.

This is a neat idea. If it were up to me to design it, I'd show it as a door made up of a grid of squares each with a single lock on them but all surrounded by one frame.

I would probably make partial doors look like normal doors, but individual locks are removed from the door and there is some rhombus pattern on the door.