Timeline rulers more explicit frame delimiters

When I zoom in enough to see frame delimiters on the ruler - per frame navigation become a little bit uncomfortable.
This is because I can not see clear seconds delimiters - all delimiters per seconds and frames are the same color and size.

Maybe you just will add gray arrows between seconds on big zomming.

See example http://imageshack.us/photo/my-images/841/rulerssuggest.png/