Is this an all the time thing or something that just happened once or twice? It is normal for stool to change a little bit if you have recently made any changes in her diet (i.e. changing from breast feeding to formula). It may just be the formula that she is on. I think I remember experiencing this once or twice with my daughter but it didn't last so I didn't panic.
Your daughter is still getting used to her new diet since she is only 6 weeks. I wouldn't panic just yet, but if it continues for more than a week or if you see any other symptoms that concerns you I would talk to the doctor. She may need to be put on a different formula or something.
I see that other moms have posted that the color is normal, I agree. But I went through a phase of having my daughter on an Alsoy formula because the enfamil irritated her stomach. I thought she was lactose intolerant, also but it turned out to be something she grew out of.