Colour-blindness support

[leighman]

The green and red used are barely distinguishable by a user with deuteranopia.
Please consider using different colours or using shapes for the three states.

[fippo]

@thefoxis can you please take a look?

[vr000m]

+1 shapes over-laying colors is the common way to do this.

[deckar01]

I can usually differentiate between green and red by brightness, but these colors are especially difficult to differentiate.

Notice that the overall intensity of the red and green hues used is nearly identical.

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Alternatives: