Most British road traffic lights are mounted vertically on a black rectangle with a white border (forming a "sighting board") so drivers can more easily look for the position of the light. In the eastern provinces of Canada traffic lights are sometimes differentiated by shape in addition to color: square for red, diamond for yellow, and circle for green (see included image of horizontal traffic light from Nova Scotia). Piloting aircraft
Although many aspects of aviation depend on color coding, only a few of them are critical enough to be interfered with by some milder types of color blindness. Some examples include color-gun signaling of aircraft that have lost radio communication, color-coded glide-path indications on runways, and the like. Some jurisdictions restrict the issuance of pilot credentials to persons with color blindness for this reason. Restrictions may be partial, allowing color-blind persons to obtain certification but with restrictions, or total, in which case color-blind persons are not permitted to obtain piloting credentials at all.In the United States, the Federal Aviation Administration requires that pilots be tested for normal color vision as part of their medical clearance in order to obtain the required medical certificate, a prerequisite to obtaining a pilots certification.
Confusion colors for red-green color blindness include:

Cyan and Grey
Rose-Pink and Grey
Blue and Purple
Yellow and Neon Green
Red, Green, Orange, BrownConfusion colors for blue-yellow color blindness include:

Yellow and Grey
Blue and Green
Dark Blue/Violet and Black
Violet and Yellow-Green
Red and Rose-PinkThese colors of confusion are defined quantitatively by straight confusion lines plotted in CIEXYZ, usually plotted on the corresponding chromaticity diagram. The lines all intersect at a copunctal point, which varies with the type of color blindness. Chromaticities along a confusion line will appear metameric to dichromats of that type. Anomalous trichromats of that type will see the Chromaticities as metameric if they are close enough, depending on the strength of their CVD. For two colors on a confusion line to be metameric, the Chromaticities first have to be made isoluminant, i.e. to have the same Lightness. Note also that colors that may be isoluminant to the standard observer (typical trichromat) may not be isoluminant to a dichromat. Color tasks
Cole describes four color tasks, all of which are impeded to some degree by color blindness:

Comparative – When multiple colors must be compared, such as with mixing paint
Connotative – When colors are given an implicit meaning, such as red = stop
Denotative – When identifying colors, for example by name, such as “where is the yellow ball?”
Aesthetic – When colors look nice – or convey an emotional response – but don’t carry explicit meaningColor blindness causes difficulty in all four kinds of color tasks. The following sections will describe specific color tasks that the colorblind typically have difficulty with.