In trying to cross-polinate for poppies, there's a couple things to think about... First off, you can only get colored poppies in the original "Classic" gardening set... not the newer looking poppies that are more spread out looking ones. The spread out looking ones that just came out this year only come in "Plain" and now Black and White through the Naturalist Quest...
Now, for getting colors in the original Poppies start with this...
Poppies
Poppies x Poppies
Snowdrops x Campion
Bulrushes x Campion
Poppies x Campion (50% chance)
Poppies x Snowdrops (50% chance)
Any of the above plants can give you Poppies seeds and the colors you get depend on what colors the partent are (and a small chance of mutants which we'll ignore)
If you want Blue (normal, not Bright Blue) poppies, you have to start with at least one Blue or Bright Blue of something on one side of one of the lists above... let's say you have a Bright Blue Campion... now with a Bright Blue Campion you can get Popies using Snowdrops or Bulrushes or a 50% chance of using a Poppies... but you need a specific color... you can't use Blue or Bright Blue of those three because any of those three in Blue or Bright Blue will give you Bright Blue Poppies... You can't use plain in any of the above, because Plain over rides all other colors and you will get plain Poppies... and you can't use another "Primary Color" (Red or Yellow) because those will combine with the Blue to give you either Purple or Green Poppies...
What this means is to get your Dark Blue Poppies if you start with a Bright Blue Campion, you need Snowdrops, Bulrushes or Poppies (50% chance) in either Orange, Green or Purple... any of those three colors in bright or dark combined with bright Blue (or any primary) will give you the "Dark Primary" back.
Please reply if this was too confusing.