I copied this from the FAQ section.

Q: What are compatibility scores and how are they determined?

For members who are open to dating, you will see that SOME thumbnails and profiles have a heart symbol on them with a percentage. This helps you identify which members are open to dating as the percent shows approximately how compatible you are with them. If you click the heart symbol on the top of their profile, you can see how it is determine. You can improve your score in general by answering all the profile questions and writing a bio.

I never noticed. Thanks.

On your page it's pink to make the boys wink. Here grey perhaps to make them rue the day. ?

It means your heart is well on it's way to being black and you're evil,.......or maybe not.