\color[<colorname>]{<text>}
is valid but you use \color without the text. To fill the missing argument context uses now the following command after \color or in some cases internal macros.
Another thing which doesn’t work in MkIV are these lines:
\definetypeface[tSCIRMA][rm][Xserif][Palatino]
\definetypeface[tSCIRMA][tt][Xmono][LM Typewriter Regular]
\definetypeface[tSCIRMA][ss][Xsans][Optima]