Hi Fabrice Thank you for your reply. It works the way I wanted. Wolfgang also replied and this has lead me to an alternative method. See my reply to him in this mailing list. Best Wishes Keith On 28/04/2022 13:45, Fabrice L wrote:

Sorry, I was a little too enthusiastic, here here is the code :

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Le 28 avr. 2022 à 08:41, Fabrice L a écrit :

Hi Keith,

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Le 28 avr. 2022 à 06:05, Keith McKay via ntg-context a écrit :

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%%%%%%%%%%%

Here is a solution, with works here, defining in another way the color «  myColor »:

\setuppapersize[A4,portrait] \usecolors[crayola] \starttext \dorecurse{2}{ \startMPpage StartPage; color myColor ; myColor := (uniformdeviate(1),uniformdeviate(1),uniformdeviate(1)); fill unitsquare xscaled PaperWidth yscaled PaperHeight withcolor myColor; 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

I forgot to remove « myColor1 » from the others parts of the code. \setuppapersize[A4,portrait] \usecolors[crayola] \starttext \dorecurse{10}{ \startMPpage StartPage; color myColor ; myColor := (uniformdeviate(1),uniformdeviate(1),uniformdeviate(1)); fill unitsquare xscaled PaperWidth yscaled PaperHeight withcolor myColor; 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[myColor, white]); fill unitsquare xscaled 5cm yscaled .5cm shifted (13cm,i*cm) withcolor(r[myColor, white]); %fill unitsquare xscaled 5cm yscaled .5cm shifted (13cm,i*cm) withcolor(r[myColor1 ,  white]); This line causes an error. endfor; StopPage; \stopMPpage }

\stoptext

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Fabrice.

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Hi Wolfgang, Thank you for your reply. I did as you suggested but it still never worked. However it did make me delve further into the Metafun, LuaMetaFun and the Colouring ConTeXt manuals where I found examples of the *resolvedcolor* helper which I used as follows: definecolor [name = "myColor", r = uniformdeviate(1), g = uniformdeviate(1), b = uniformdeviate(1)]; for loop.. fill unitsquare xscaled 5cm yscaled .5cm shifted (7cm,i*cm) withcolor(r[resolvedcolor("myColor"), white]); endfor; I also found the *namedcolor* helper and I could use it as follows: fill unitsquare xscaled 5cm yscaled .5cm shifted (1cm,(2*i)*cm) withcolor namedcolor("myColor2") ; However, for some reason it did not work in: fill unitsquare xscaled 5cm yscaled .5cm shifted (7cm,i*cm) withcolor(r[namedcolor("myColor"), white]); // Thanks again for your suggestion// Best Wishes Keith// On 28/04/2022 16:04, Wolfgang Schuster wrote:

Keith McKay via ntg-context schrieb am 28.04.2022 um 12:05:

...

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) ] ;

Remove the backslash in front of the definecolor command.

Wolfgang