I've always thought that the plain black-and-white banners/arrows with Kansas SR shields looked a little weird. South Dakota, Vermont, California, and Wyoming use colored ones to match their shields, and Louisiana used to before the switch to black-and-white shields. Minnesota uses blue-and-white ones, but those are already standard for Interstate use, too. (Although it'd be pretty neat if MnDOT switched to specialty ones that have a gold border (and maybe also the legend) instead of white, but I'm digressing.)
So, is there a reason they don't use colored ones?
I've never been to Kansas but my only guess is it would look too much like caution yellow, given that the state route shield is yellow.
In addition to the caution color thing, I expect cost may be a factor.
The only way I have seen yellow banners used is when they say "TOLL", which might also add an element of confusion for drivers who may be familiar with these signs.
EDIT: totally forgot about Wyoming.
Wyoming uses yellow banners/arrows, though, but the state apparently doesn't suffer from severe problems.
AFAIK, there isn't a specific reason for not using yellow-background tabs that KDOT has released into the public domain, but I think keeping standard signs off-the-rack as far as possible is a factor.
The current set of route markers with black backgrounds dates from the 1960's. Before that time, Kansas used regular-size markers on cutout blanks and oversize outline markers on 24 in square blanks. Specifications for both are given in the 1949 Kansas MUTCD (Kansas was at one time an own-manual state; I don't know when that changed, but Kansas is now a direct adopter). In the case of the oversize markers, the 1949 manual calls for overall white background for US route oversize markers, and yellow for Kansas route oversize markers, but black on white for all auxiliary tabs, both regular-size and oversize, regardless of whether used with a US or Kansas route marker.
I don't know if there was experimentation with colored tabs alongside colored US route shields when those were used in the late 1950's; Richie would be the one to ask.
I am not certain if this is something that KDOT took into consideration, but on states using black-and-white plates for state highways, there is a little bit of a "highlight" effect when an Interstate is included in an assembly with a large number of highways. The blue plates make the Interstate stand out.
Quote from: J N Winkler on June 18, 2017, 11:14:47 AM
I don't know if there was experimentation with colored tabs alongside colored US route shields when those were used in the late 1950's; Richie would be the one to ask.
I'm not aware of any use of colored US route shields besides US 56 (BTW, It appears that they had used the green markers for US 56 from the outset until KDOT switched to the standard shields in the 90s.) The only photo I'm aware of of a green US 56 shield "in the wild" with an auxiliary marker has a black/white auxiliary marker [specifically, a M6-6L].