paint.net is a great paint program for doing this sort of stuff, and its totally free
https://www.getpaint.net/
there is a great site with logos / fonts / colours from Elite, EDAssets.org
Gonts used are Century Gothis
Euro Cps
Eurostyle Roman
Sintony
Telegrama
ED assets has got your colour hex codes, which if you goolg the hex colour you get the other value schemes,
Red Green Blue / Cyan Magenta Yellow blacK / Hue Saturation Vibrance / Hue Saturation Luminesence
so you can plug these values into your program and get the exact shade of the colour for things like fonts etc...
https://www.google.co.uk/search?q=#029e4c&cad=h
So googling the green for friendlies on the scanner's hex value from edassets gives you this screen:
Now its just like any other poster, its on your imagination and graphics / computer abilities, but the info I've posted here whould help you to get the right colours and the right typefaces and the right logos to enable you to make something semi official looking.