koala

Hi pianogirl, welcome to TSF

The 2 colours you selected for the cards, deep green and blue, may not offer enough of a contrast for the barcode scanner to read, which is why barcodes are usually black on white.

I don't think a different ink would make any difference as inks for specific printers are generally the same in quality.

Instead of adding a white label, I would go back to using white card to print on, and then use some other method for class identification. Maybe a coloured strip along the top of the card or a coloured border.