Firstly....how do I know what i'm buying is really green shrimp? If these guys react to shipping colour-wise like cherry shrimp i'm assuming the colour will be very faded or even see-through?
For Green shrimps, they will bring back their green color (from almost clear) once you acclimate them well in your tank with a pH of at least slightly above 7 and at least semi-hard water. If they are from imports, then your possibility of getting pure Green shrimps are very low along with the fact that they are healthy - like playing the lottery!
Most of the Green shrimps that are imported are also mixed with Rainbow shrimps and they could be of any color - check "Shrimp Varieties".
And they are mostly females and unhealthy. If you read my previous threads about Green shrimps, you will read that I had 1 really bad experience with an importer of Green shrimps. All dead and spent too much money on it with nothing to show for - actually they were mostly Rainbow shrimps. If you do receive healthy shrimps and they do survive after a while, then one of the easiest way to observe is the female ovaries. If the shrimp is light to dark green in color, their ovaries should be a very nice bright green color like Mustafa's green shrimps. And their eggs should be that same color in the early stage. I hope this helps to answer part of your question.
To answer the 2nd part of your question: Yes green shrimps "can" live together with Amano shrimps. However, the Amano shrimp are more aggressive than Green shrimps and it would be very hard for Green shrimps to compete for food when it comes to feeding time.