I don't think, the old Airfix kit is that accurate, but good luck anyway, practice never hurts! As for the paint scheme, I don't know what paints you like to use, but all i can find is Humbrol enamel colours. For the underside, Humbrol No 65.
For the top, some 217's were RLM 70/71 while others were RLM 72/73. It seems to be that the demarcation line between top & bottom colours makes the difference, if it's halfway up the fuselage, then use the maritime scheme of 72/73.
The Olive green is near to RLM 80. I don't have a conversion for the other RLM numbers, hopefully someone else does. Though Polly scale paints list the folowing if it will help; RLM 70 - blackgreen, 71 - dunkel (dark) green, 72 & 73 are just listed as green. sorry I can't be of more help.