[Retros] Coloring + add units?

[Mu-Tsun Tsai]

Hi everyone,

Speaking of coloring problems, I was wondering if there's any problem so far 
that comes with the stipulation of "color the pieces and add the missing 
unit(s)"? I know there're a few coloring problems that specify the number of 
units to be added, but I couldn't find an example with just "add unit(s)". 
At least PDB don't have one under the key words "coloring problem" + "add 
pieces". Any idea of this? Thanks :)

Mu-Tsun Tsai