Removing entries in a drop down field dynamically

I have a series of drop down fields, all initially with the same data populating them but once the first field is selected the client would like that selection to no longer be available in the next drop down. Not sure how to create lists for drop down on the fly, or is there a better way to approach this....?
 
The options available would look something like this:
 
Field 1 choices: Blue
Green (selected)
Yellow
Red
Orange
 
Field 2 choices: Blue (selected)
Yellow
Red
Orange
 
Field 3 choices: Yellow
Red
Orange
 
Any ideas?