[NTG-context] macro string in metapost

The goal is to make the following string in metapost: string s; where s must become "\MPcolor{Blue}". and ultimately execute this at the right moment with: scantokens s; The following makes s = "MPcolor{Blue}": s := "MPcolor" & char oct"134" & char oct"173" & "Blue" & char oct"134" & char oct"175"; But I seem unable to add a \ in front of it without expanding the string by TeX. Thus it does not work to put: s := char oct"134" & "MPcolor" & char oct"134" & char oct"173" & "Blue" & char oct"134" & char oct"175"; Placing a \noexpand in front does not help. How to? Hans van der Meer