Accessibility: increase color contrast
This issue originally was at https://github.com/framasoft/framadate/issues/66
The Green-Orange-Red colors choosen to indicate if someone is available/possibly available/not available is not much contrasted. Color-blind people might find it complicated to differentiate between answers.
This is part of the general question of accessibility. If this brings up other issues, I will try to provide some help on this.