There are no fixed rules here. Continue your service to the site and who knows one day you would see your name in Pink.
Go through the words of the moderator on the same:-
Admins are not appointed based on their contributions to the site. All members are expected to receive as much or more from IRI as much as they give. This equilibrium is very important for the sustenance of this site, as well as your interest in this site. If you find that there is an imbalance, and you are contributing/blogging...
more...

more without receiving any reciprocal benefits from this site, at that point, this site ceases to be of benefit to you, and you should discontinue your participation.
Members are appointed Admins on recommendations by our current Admins, based on their courtesy, politeness, maturity and other social qualities. Rail knowledge or contributions to site are not yardsticks for Admins. Many of our Admins may not know much about the Railways, but they are Admins based on their general social qualities. It is very likely that you have the above qualities, but our members are not familiar enough with you to recommend. In such a case, you may just continue participation with the site, and eventually someone will recommend you.
Thanks.