How to make users auto-transit between groups?

I'm having issues finding a way to enable auto-transitions between successive groups, as per the post count these users accumulate.

For example, on my forum, under Group Administration panel, I've six successive groups that are defined by auto-subscribe minimum posts, respectively 0 (for newbies with restricted rights), 2, 50, 500, 2500 and 5000. Now, what I don't see as effective manifestations is the colour of group members, for which I've specified in each group and on user options panel where I've ticked 'colourise usernames'.

Still, everyone, administrator included, is still coloured that of newbies group and all users have made at least 2 posts but still do not get colour of second group onwards!

Can anyone fix it please?

It depends on the order of the groups.

Administrators - 0 - Red
First Group - 1 - Blue
Second Group - 2 - Green

A member is in both the first group and second group, but they will be the color of the first group.

Also the groups have to be open or closed, not hidden.

Yes, all my first five successive groups are assigned group order, respectively as 1, 2, 3, 4 and 5, where Administrators are set to 0.

Still, colour changes are not effective.

Now that you mentioned group order and how colour will stay depending on which comes earlier, I've now fixed it. Thanks!