It's all about readability in a parking garage. Many drivers are completely stressed with the situation of driving their expensive symbols of freedom in circles through narrow spaces. As this alone requires full attention, not much capacity remains brainside for overall spatial orientation.

Keep it simple, keep it bold.
Freedom will be grateful.

Colors are great – when your eyes can see them – but we talked about this already here. Cognitive abilities differ and you never know who might face a sign with what motivation in mind.

It seems like a great idea to give the colors a little buddy named "icon". Together, they are ready to fight against orientation confusion and to leave nothing uncertain.