Shrimp sold in North America as 'Ghost Shrimp' are most likely to be Palaemonetes paludosus. However, many Macrobrachium shrimp, in their juvenile post larval state, appear exactly like adult Palaemonetes paludosus.
Palaemonetes paludosus commonly have spots of pigment, orange, yellow, white, and other light colors. Most frequently it's concentarated on the tips of their claws, and tail.
However, people have fairly frequently aquired Macrobrachium shrimp when they thought they were purchasing common Ghost shrimp. Many Macrobrachium species slowly develope color as they mature. There are species that are blueish, to dark blue. One notorious species that gets blue is Macrobrachium rosenbergii. They will get very, very large (approximately 12 inches, not including their claws), when full grown. They are also extremely aggressive.
So, watch your blue shrimp for signs of aggression, and for continued growth. If the shrimp starts to attack other aquatic fauna, you many need to take steps to prevent an invertebrate slaughter.
Good luck.