The color of the titlepen does not work

[cvgmt]

We try to change the color by titlepen=fontsize(50)+brown; but it seems that the brown not work. ( version 2.92 )

`settings.tex="pdflatex";
orientation=Landscape;
import slide;
viewportsize=pagewidth-2pagemargin;

usersetting();
titlepen=fontsize(50)+brown;
itempen=fontsize(30);
import x11colors;
fill(background,box((-1,-1),(1,1)),Azure);

titlepage(title="A Demo",
author="",
institution="",
date="\today",
url="https://asymptote.sourceforge.io");

title("The titlepen not the brown");
`

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