It is because your wheels lay the grass down and the sun reflects off it differently... This is how you stripe you grass if you get a striping roller.. here is my front yesterday after striping... you are doing the same thing with just the wheels..

 

If I look closely those lines are physically darker green than the rest of the grass. I cut the grass 3-4 days ago so none of the grass looks to be laying in a different direction, its all fairly straight up.
Also, it seems like the dark green grass lines are taller/grew faster than the rest.

 

I'm not a pro, but in my opinion look like you always mow in the same direction, try mowing different direction that works for me but my yard is way much smaller. just my opinion may work.

 

If the grass along the wheel tracks is taller because it never got cut fully it might be greener. Generally taller grass has a darker green look to it.

 

If I look closely those lines are physically darker green than the rest of the grass. I cut the grass 3-4 days ago so none of the grass looks to be laying in a different direction, its all fairly straight up.
Also, it seems like the dark green grass lines are taller/grew faster than the rest.

When was the last time you fertilized and what method?

From what you've said and the picture it sounds like it may be the same problem I've had before with fert spike.
My spreader was broken (crappy Scott's mini edgeguard) and it was dropping concentrated lines of fertilizer which led to chessboard like patterns and darker faster growing lines of grass.

 

If the grass along the wheel tracks is taller because it never got cut fully it might be greener. Generally taller grass has a darker green look to it.

+1^
Also, if you made any ruts while mowing during wet periods, those areas will tend to collect water during future rain events (thus, staying greener). As others have mentioned, altering mowing patterns will help to reduce both the higher uncut blades and rutting.

 

Cut diagonally the next few times and see if it's related to mowing. It looks odd, like it repeats every 3 rows.

 

Cut diagonally the next few times and see if it's related to mowing. It looks odd, like it repeats every 3 rows.

That was my thinking, my last cut was width ways (left to right in the pic) and you can slightly see the dark green lines going that way too. It seems to be every 2-3 tracks of the mower.
With the rain we are getting it may go away and blend in. Ill try diagonal next cut and report back.

 

That was my thinking, my last cut was width ways (left to right in the pic) and you can slightly see the dark green lines going that way too. It seems to be every 2-3 tracks of the mower. With the rain we are getting it may go away and blend in. Ill try diagonal next cut and report back.

I am using a riding mower this year and the lawn looks like a carpet once mowed as compared to my push mower that left deep wheel marks and footprints ; both very noticeable afterwards especially when I'd mow high. I'll never go back to a push mower.

That said, I have noticed some green streaking a few days after mowing now too. I think it is due to the front wheels of the rider pushing down the grass and then the suction from the deck, set on HIGH, not being able to lift the smashed grass back up fully as it cuts as compared to the grass in the center of the row; therefore resulting in an uneven cut.

A compounding factor is the tendency of rider owners to drive far faster than we should (since it's fun), not giving the machine enough time to suck up the smashed grass fully prior to the cut. I side-discharge too, so the suction is not as strong as if I were to use mulching blades.

The green streaking I see is noticeable once the smashed grass has time to pop back up, with these blades appearing greener because they are indeed taller than the grass in the center of the row.

I'm going to try to drive slower next time to see if the green streaking I see is reduced.

Good topic!