Here is a Frequently Asked Question...
" I know the brief says we can only use two colours but do shades of the same colour count?"
And here is the answer from Bob...
"In screen printing, separate screens have to be made for each individual colour or shade of colour and so even shades of the same colour will count separately.
Thus, if you wanted to use maroon, red, pink, and baby pink - this would count as four colours and not just all as one colour in different shades.
You can only use two colours for your design.
I hope that answers your question clearly."