Matt,
the official color for the blue areas is FS35044, commonly known as "Insignia Blue". Depending on the paint manufacturer, it might be called "Signal Blue" (Vallejo Model Air 71.091), or just "Blue" (Gunze H326).
Don't know about the Vallejo's accuracy, but I was rather happy with the Gunze color's look - the markings on this Navy Sopwith Camel are painted using their Blue and Insignia Red H327.

1 attached image. Click to enlarge.

Thanks much. I was assuming Vallejo 71.091, but wanted to throw it out to the group. BTW-nice Camel. Rigging looks really good.

Thanks guys. Running the risk of hijacking Matt's thread here... 😀 Bernard, the grey I used is Gunze FS36231 (H317). Couldn't figure out what exact color was used back then, so I went with a resaonable guestimate of something haze-greyish. The side serial is a custom mask I created by analyzing some grainy pictures and drawing a template, then cutting it on my Silhouette cutter.