Autocomplet with no previous values
 

I have a series of cells that I want to only accept predefined values from a list
I have set this up through the list option in validation which is working fine

However, say if the list contained text values such as red, yellow and blue. How can I have the cell recognise these as r or y or b
I know autocomplete does this but only is there is another entry in the column already.

eg If there is no entry for red in the range then how can i force r to = red

Bria