Patch 38 now also replaces the /ColorSpace of a shading that is
DeviceGray, DeviceRGB or DeviceCMYK with the default for it, whether the
shading is painted by sh or as a shading pattern. Poppler and MuPDF draw
these in the default too. The shading's cache key includes the default,
as the image's does.
The forms test also covers a form whose /ColorSpace has no default: it
draws in its page's, as in Poppler and MuPDF.
Guillem Hermida
4ce3e4f23b