Section 4.5 of the PDF reference says: "Color values are interpreted
according to the current color space, another parameter of the graphics
state. A PDF content stream first selects a color space by invoking the
CS operator (for the stroking color) or the cs operator (for the
non-stroking color). It then selects color values within that color
space with the SC operator (stroking) or the sc operator (nonstroking).
There are also convenience operators—G, g, RG, rg, K, and k—that select
both a color space and a color value within it in a single step."
Previously, those convenience operators did *not* set the color space.
This commit, following on filed issue #779, fixes this. It also adds a
test to demonstrate that, at least for the do_rg method, the fix works
as intended.
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