Mostly what looks good to you, because every photo you look at the color will appear a little different. Here are some suggestions:
Gunze (GSI Creos) 338 light gray
Model Master 36495 light gray
MRP 36495 light gray
Next two are SLIGHTLY darker:
MRP Boeing 707 gray
Model Master Voodoo gray
Here’s another method using Testors paints in the small bottels. Using gloss white and 1138 gray, mix 1 part of 1138 gray to 6/7/8 parts gloss white. The 6/1 mix is close to 707 gray while the 8/1 mix is close to the above listed light gray paints. Keep in mind that these differences are subtle, but one may look better to you than another. Hope this helps.