What does your soil test say?

 

I would get a soil test. Fe and pH both heavily affect color. Ironite is not very useful at high pH. Until you get the results back, you can spray foliar Iron +/- Ammonium Sulfate.

 

Does it look darker green before you mow?

 

You need to determine the ph and iron level in the soil. If your soil was like mine it's probably lacking in iron. Unless you or previous owner applied iron every few years it probably has no iron. The only way to know is with a soil test done in a lab. It must be done in a lab because you need accurate pH. Once you get this back you can apply some ironite which has 5% sulfur I think to help bring the pH down. Don't apply sulfur or try to make big pH corrections without consulting with some people on here first

 

I thought it is typical PRG green? I'm not sure about this certain variety. Was is darker before?
I have PRG/TTTF mix and my Torsion and slider LS PRG have similar green. I remembered the seedlings was dark green when first sprouted, and became to lighten to this green the next spring when it is established

 

You should try using Chelated Liquid Iron instead Ironite. Granular Iron will take a while to be absorbed by the plant, at which time, if you're constantly cutting and collecting your cuttings, you might find you never get the level of green you want.

Granular Iron can also lock up in the soil where soil gets filled with balls of Iron that prevent the roots from getting moisture and nutrients from the ground. This happens when too much Granular Iron is put down too often.

Liquid Iron and, more importantly, Chelated Liquid Iron is applied directly to the grass, making the results almost instant. You'll see your lawn turn green overnight. It's also much harder to overapply, meaning you keep applying until you get the level of green you're after with little risk of damaging your lawn.

Chelated Liquid Iron is the most expensive option but comes with the least risks and the fastest results.