MRE:

my_pal <- colorRampPalette(c("red", "yellow", "blue"))
tinyplot(
  1:10,
  by = as.factor(1:10),
  palette = my_pal
)
# works
tinyplot(
  1:10,
  by = 1:10,
  theme = list(palette.sequential = my_pal)
)
# works
tinyplot(
  1:10,
  by = as.factor(1:10),
  theme = list(palette.qualitative = my_pal)
)
# fails

Use-case context:

I initially set palette.qualitative as a vector, but then kept getting the recycle warning when I had more groups than elements of that vector. So I wanted to build a function to programmatically generate an arbitrarily long list of colors that are not necessarily a gradient. I'm not sure how I can set a custom palette.qualitative that is distinct from palette.sequential and also supports arbitrary many groups.