it goes in blue, comes out with a green tint, my mech says he's sen it before (different plane) what is causing this?

Get some new bladders...
-Zach

Don Ho.... Tiny Bubbles...in my wine, make me happy make me feel fine... perhaps they make your fuel green too...

Sorry couldn't resist... Zach knows!
Jim

I forgot to say I just got new bladders

OK,
Lets look at this with all the info before I shoot my mouth off again. You have NEW bladders (all 4?) or rebuilt? The fuel that is "green" is coming out of the fuel strainer...both or just one wing, or one tank? Are the tanks full or left partially empty? Where are you located? Is the plane hangared or outside? What kind of fuel caps do you have, and are the TIGHT? How often do you fly/refuel? Are you adding anything to the fuel (MML or like)? Is this the first tank of fuel since new bladders?

The dye used in the fuel is blue dye. It can combine with yellow varnish, or other oil substances that look yellow, and you get green! Many sealants will give off yellow tints to solvents. Also extreme evaporation will cause an elevated concentration of dye (fuel evaporates, dye doesn't demonstrated by blue fuel stains) and this looks very dark blue, and can look green in some drain sampler glasses. If you are in the habit of leaving tanks mostly empty, have a hot climate and a poorly sealing gas cap, you can evaporate all of the gass in a tank in less than a week. It leaves behind all of the old dye and varnish (yellowy brown), and when you refuel, voila you get really green fuel! More than not this happens with old bladders as the evaporation happens through the bladders.

-Zach

All 4 new bladders,green is coming out of the strainer, left side 1/2 full tanks, the plane is hangered, webco fuel caps,
still breaking in the engines (but that's another story) I'll say it the 3rd or 4th tank since new bladders

OK,
Its coming out of the left strainer, which tank? Run the drain long enough to purge the fuel from the main and check the aux. See if you can isolate which tank. Once you isolate it, drain it, replace the fuel and see if it goes away (you can use the drained fuel in some of the other tanks...for St Pattys day :-0). Honestly, I think it is a contamination issue of one of the tanks, and you should drain and flush and see if it gets better. Check the vent lines and make sure the caps fit TIGHT and the cover door gaskets are in good shape.
-Zach

Recently I drained blue fuel into my normal container (used for a couple of decades now) and then picked up the container to check for contaminants and saw green, cloudy fuel. Amped up my blood pressure, for sure. A first fuel drain result of this type in 40 years. Hav had other stuff but not this.

Then, I remembered I'd dislodged a mud dauber's nest on the right exterior of the right main gear area - they can build amazing things overnight - I thought some dust might have drifted into the fuel.

Sure enough, I drained again and checked tank by tank - it was clean blue fuel.

As Zach commented, it could be a number of things - just thought I'd mention this recent event in case it might explain your results - maybe, maybe not but there could be dirt in the drain tubes or in the sump system - especially if it has been worked on recently - wonder if the sump area got new gaskets or if dirt is getting in?

Hope something in here helps.