Recognize grass-fed beef? I am in the process of losing weight and I am using a meal prep service to help me with portion control. I choose the ingredients, order online and they deliver via fedex. One of the options is to order grass-fed beef and, naturally, there is a premium on this meat (and the meal prep service is not cheap to begin with!). 

So, when the meal is in a cooked state, how can I verify that they are sending me grass-fed beef? Are there any markers/taste I should be looking for? The service has a good reputation, but I just want to be able to verify that I'm getting what I paid for.
Grass-fed beef will have yellow fat rather than the white fat of grain-fed beef. This is because of the beta-carotene in the grass, apparently.