While I understand the function of a relay I haven't the slightest idea why some are yellow and others are green in the D1.

I'm guessing they are run of the mill relays with a specific amperage rating. I need to replace my ABS relay (K101) and perhaps K102 and K103.

What should I use?

 

Relay specs are : Coil voltage, contact amperage, switching mode (or form), and number of poles (contacts).

Use same coil voltage, same or larger contact amp rating, and same form, and same number of poles (to fit in the same base).

Some relays energize to close a contact, some energize to open a contact, and form C contacts switch from one side to the other.

Generic cube relays are typically rated 30A contacts, 12 - 14 volt coils. Available from auto parts stores or online.

Sometimes the contacts wear out from arcing or melting if switched a lot. The contacts can be cleaned up with a small file, then re-used if the coil was not burned up. Just pry open the plastic cover off the base. Then maybe swap the refurbished one for like model of one that is rarely activated, for example ABS relay swapped to a mirror control relay (just an example to make a point, I don't know if they match). Hope this helps.