When planning a stamp issue, many factors have to be considered (not least UPU regulations). Colour is, of course, one of the main variables. It is all very well to compare colour samples laid out on a table, but there is no substitute for seeing what a projected design would look like in various colours when actually printed. Colour trials were created to solve this so that impressions could be taken from the original die for comparison purposes, very often of the same value (so that there would be a level playing field) for the approval of the authorities. As such, stamp proofs may often be found in unissued colours, perforated or imperforate.