BaseConverter

From Fmepedia

BaseConverter is a Workbench Transformer. Converts numbers to a different numerical base, by supplying the original base and the desired output base. The most common values for base will be 2 (binary), 10 (decimal) and 16 (hexadecimal), with 8 (octal) trailing behind.

This way you can for example convert a Microstation color to a KML color. Expose the igds_color.red, igds_color.green and igds_color.blue attributes. Set up 3 BaseConvertors and have them each convert one of the color values from base 10 to base 16. Then use a Concatenator to combine the three color strings and add an additional ff to the end of it.