Anybody know how to tell the difference by looking at them?

Are they different colours?

I went to buy some 91 standard (benzene) in a plastic fuel container and when I got home it was a green colour.

I thought the 91 benzene (91 tamada) was red???

Color varies by brand.

Color varies by brand.

i have never bought benzine 91 that was green

Don't worry, you can trust them. No, really!

I bought some 91 a couple of weeks ago that was sold in whiskey bottles at some little hilltribe store and cost 95 baht a liter. I was way out in the middle of nowhere up by the Lao border somewhere east of Chiang Rai and running on fumes. 95 baht seemed dirt cheap compared with the alternative of walking. I figured 41 bought was for the fuel and 54 baht was a stupid tax for not filling up at a pump when I had the chance (had half a tank). Who knows what was in those bottles, but I didn't have to walk.