The card is legit, no missing color etc.
My guess is cut from a sheet, all known P150 Planks are handcut or scrapps in some shape or form.
The nicest of the bunch is the sheet mate to the famous T206 Wagner PSA 8 (also P150) and was sold by REA for 100k used belong to Charlie Conlon sold to him by none other than Bill Mastro, and is IMO the nicest Plank in the world.
http://www.robertedwardauctions.com/.../2009/890.html
The other is from the Halper collection pictured here (white,missing blue). Also handcut. The other Halper card missing color (with blue) handcut is a Sweet Cap back.
This makes number 3...
Easily the second nicest one after Conlon's card.
My thoughts were for some reason Plank P150's were not issued and the ones we have today are handcut ones that escaped the factory...but who knows perhaps a factory cut P150 Plank is waiting to be seen by us all someday...
Also 150 series Planks are always the best looking sharpest cards of Plank minus the Halper examples above. There are less 150's floating around and way more 350's. The 150's are much more desired by collectors for this reason and will sell for more when offered.
Cheers,
John