consistency in call-to-actions

Do you have the feeling something is wrong here? 

facebook add members to group
facebook user requested to join a group. This is how it looks like when you approve them

I do. Buttons in your website design should not confuse you, but to be consistent. If colours and contrast are involved, they should not give you mixed signals. When we talk about user experience, this is a very bad example: first, the dark blue button is connected to positive action that is expected of you (“Approve” definitely gets user’s attention first). Then, all of the sudden, the negative (“Cancel”) button is coloured that way.

Make sure you keep consistency in the call-to-action buttons on your online space. For example, colour all of the buttons that lead to a registration in blue; and colour all of the error messages, or cancel buttons in red or else. This way the user will always know what it is about, even before reading the text on the button.