If you already have R,G & B color codes:
Use Windows Calculator to individually convert RGB values into Hex.
Type in the R,G & B codes one by one into the calculator in DEC mode. Note the Hex value in a table. Once have all 3 hex values, you can string them together for the tools mentioned "0070C0" what you get when you concatenate the values together. Prefix it with #FF for Metro Studio and just a # to use with HTML/CSS.