introduction
construction
weight
contrast
colour
stripes
measures

Everyone understands that the colours of the shirt numbers should contrast from the colour of the shirt. What should be kept in mind is that light figures on a dark background look bolder than dark figures on a light background. This effect is caused by radiation of light areas over dark areas.
So, theoretically spoken light figures on a dark shirt should be drawn somewhat thinner than dark figures on a light shirt. In practice this can be too complicated. But when one must chose a suitable weight for shirt numbers it’s important to look at the effect of changing background and foreground colours.
When the colour of the shirt is neither dark nor light, a small dark contour round a light figure can accentuate the form.

The black figures (left) look somewhat thinner than the white figures on a black background (middle). A contour accentuates the form (right).