It's not unheard of. Early Allison-powered mustangs had them. Many P-47s in the PTO had them. Even some P-51Ds (and/or later marks??) had similar stripes.
Not too much of a stretch to see them on a B-25. Only, most of the ones I've seen are white (over OD) or black (over NMF). Blue is a bit odd, and may be an interpretation or artist error.