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Hi, In the MWE below I define an rgb colour, myColor1, using random numbers for the r, g and b components. I then use it to fill a unitsquare the size of the page, which works as expected. In the loop that follows I then use the defined colour, myColor1, along with white and the variable r to create shades of myColor1 as in the MWE below. However, myColor1 is not recognised in the loop and seems to be replaced by black, although if I use a predefined colour, in this case BurntSienna from the crayola collection, it works as expected. I have tried a number of ways to get this to work as shown in the code but without success. I would be grateful for any suggestions. Best Wishes Keith McKay %%%%%%%%%%%%%%%%%%%%MWE%%%%%%%%%%%%% \setuppapersize[A4,portrait] \usecolors[crayola] \starttext \dorecurse{10}{ \startMPpage StartPage; \definecolor[name="myColor1", r = uniformdeviate(1), g = uniformdeviate(1), b = uniformdeviate(1) ] ; fill unitsquare xscaled PaperWidth yscaled PaperHeight withcolor "myColor1"; for i =2 step 2 until 10: r := i/10; fill unitsquare xscaled 5cm yscaled .5cm shifted (1cm,i*cm) withcolor(r[\MPcolor{BurntSienna},white]); fill unitsquare xscaled 5cm yscaled .5cm shifted (7cm,i*cm) withcolor(r[\MPcolor{myColor1}, white]); fill unitsquare xscaled 5cm yscaled .5cm shifted (13cm,i*cm) withcolor(r[\MPcolor{"myColor1"}, white]); %fill unitsquare xscaled 5cm yscaled .5cm shifted (13cm,i*cm) withcolor(r[myColor1 , white]); This line causes an error. endfor; StopPage; \stopMPpage } \stoptext %%%%%%%%%%%%%%%%%%%%%%%%%%%end MWE%%%%%%%%%%% I am running: system > system > ConTeXt ver: 2022.04.20 19:18 LMTX fmt: 2022.4.26 int: english/english system > system > 'cont-new.mkxl' loaded