Gridfinity bin for my 1x3 Mr. Pen Sticky notes (Amazon link).  I have some gridfinity bases glue onto my desk for easy organization, and I find that a 1x3 sticky note is more useful than a full size.  I did manual filament changes as I don't have an MMU.  I put transparent layers between the color changes as I thought it would lead more to a gummy candy look.