Everyone's favorite poppies are now easy to grow with potted seedlings; HOWEVER, this is a mix and the color CANNOT be guaranteed.  I recommend you get several to increase the chances of getting more colors.
 
Poppies love cooler weather and will give stem after stem after stem around May.  Cut the stems with the bud cracks open enough to see the color.  
 
Plant seedlings about 6-12" apart and keep the well watered until rooted.  Plants grow to about 15-20" tall.  They like to reseed so either save the seedpods or let them reseed on their own.
 
Seedlings come in a 2.5" pot.
 
There is no refund or warranty on plants after purchase.