I have enlarged the pic of the "12" and have to say that the yellow colour for the number is more than very possible. The enlarged part shows the yellow triangle of the fuel octane being dark. Also here is another "1" of the unit. Also here the fuel marking seems to be dark similar to the "12". This may indicate the yellow colour for the numbers though.
Also had a close up to the "1" posted in #5096. The enlarged pic shows something that like the dark fuel marking. That also may indicate the yellow colour for the digit. I have found a couple of sources more for the pic and all stated the yellow "1".
To sume up... the pic with the "13" posted has been titled "Yellow 13" while being saved on my HDD a couple of years ago. Although it looks like the number was of the red colour , the yellow one seems to be more than possible. That's a pity we can't see the port side of the kite. The tone of the fuel triangle would give us a clue of the negative type the pic was taken with.
Just about the right size for getting around town, or the supermarket, with no worries from women and shopping trolleys getting in the way.
"Wo ist der bacon - vorwarts !"