Borrowing from amr's answer here
ToExpression["16^^" <> #] & /@
Partition[Characters@StringTrim[#, "#"], 2] & /@ {"FFFFFF",
"#FFFFFF", "000000", "#FF5500", "#005500"}
=>{{255, 255, 255}, {255, 255, 255}, {0, 0, 0}, {255, 85, 0}, {0, 85, 0}}