I wonder whether the information about red dye being residual is correct ? AFIK, steel does not absorb dye.
If you were a regulatory officer, you would want the public to believe that dye was clingy, wouldn't you ?
Plastic sight pipes, perhaps, but bulk tanks, No. Otherwise all the marinas will have to replace their tankage.
SB, get the tanks emptied (I'll take the red diesel away for a small fee ) and get the yard who do the job to certify they have emptied the tanks completely on the invoice.
I think, therefore I am. I am, therefore I sail.