Clan tartans are one specific thing that are best not mixed at all unless they are different setts or color ways of the same clan (approved clan tartans). The highlander way, one person one clan allegiance, one tartan (or limited collection of that clan's approved tartans) in kilt and/or other tartan accessories, one clan's other non-tartan clan identifying accoutrements (cap badge, kilt pin, lapel pin, etc...).
Diced hose are not clan specific (to the best of my knowledge) regardless of whatever two colors are involved in that dicing. Red and black diced hose are probably the most ubiquitous of all color combinations available in diced hose, and despite their apparent similarity to any tartan they are not related, although through military unit designations some diced color combos are more commonly seen with certain tartans that were used for military unit standard uniforms, this use of tartan is for military conformity rather than clan allegiance purposes.
Any color combo of diced hose can be worn with any tartan IMHO although certain combos may be more appealing than others from a stylistic standpoint, the Highlander way saying only that diced hose (probably simply because of their relatively higher cost and seemingly dressier appearance than solid color hose) are better reserved, in general, for special occasions or dressier events than for daily wear usage, but this is by no means absolute. Certainly not as absolute as not simultaneously wearing items identifying distinctly different clans such as clan tartans and badges and such.
We outlanders are typically less directly attached by time and mixed heritage to a single clan, and more likely to desire to "honor" more than one family/clan name in our family tree other than our strict paternal lineage (the highland way) by owning and wearing multiple clan tartans, but we should IMHO not mix clan identifiers in simultaneous wearing.
As my lowland family had no tartan until late in the 20th century, although I sport both tartans of my modern day clan, I also sport multiple versions of Douglas clan tartans, as historically that was the major regional clan with which my family was most typically affiliated, and if my family ever wore tartan in the old days it likely would have been Douglas or none. Otherwise I typically stick to district or fashion tartans of no historic clan affiliation.