The question "http://scifi.stackexchange.com/questions/112626/why-do-han-et-al-go-to-maz-s-castle-on-takodana" has a good answer about ditching the Millennium Falcon because they know the First Order is looking for it in association with BB-8, Rey, and Finn, but given that BB-8's orange color is described as unusual[1] for a BB-unit, why don't they paint him or something?

[1] "He’s a BB unit. One of a kind. Orange and white. Utterly unique and utterly invaluable." --Poe

EDIT: Of possible related interest, C-3PO has a red arm in TFA (see Why does C-3PO have a red arm in “The Force Awakens?”), which could be a sign that droids can be painted, or a sign that they can't (e.g. if it's salvaged from a red protocol droid).