Even bluray needs chroma upscaling when displayed @1080p. Luma upscaling is, of course, not needed.
For the same reason chroma is stored at a lower resolution, even on bluray (human eyesight is less sensitive to chroma than to luma) the more advanced, more intensive, upscaling methods (especially jinc) offer less benefits than for luma, so many are quite happy with jinc 3-tap with AR for luma and bicubic-75 with AR for chroma.
With your card you may be able to use Lanczos 3 or 4 tap for chroma or even the same jinc settings as for luma, but jinc for chroma can push weaker cards over the limit, especially for interlaced 30fps content. You will need to try and see. I wouldn't expect you to see a big difference when actually watching a movie between any of those chroma settings, although you might in select still frames.
There is no need to go higher than 3-tap for jinc. It may even be worse if you do.
