The problem has to do with the INTENSITY of the colors. The grey doesn't project the same color intensity as the green and pink. You need to find a color (choc brown would do) that isn't overpowered by the other colors.

ditto

I'd replace the green. The tone isn't quite the same as in the striped fabric.

I personally would use a softer green and purple in any range from lavendar to a medium purple. I think I have that fabric, hope you show us what you made.

What are you making and any particular reason you have chosen all solids to go with that gorgeous stripe?

Dark steel grey for contrast - black would be too strong with those colours.

BLACK....BLACK...BLACK....BLACK...BLACK

I've been taught to have contrast - a dark color is needed to make the lighter colors pop. I like the stripe.

I think black would look awesome.

Personally, if you are using the stripe, I don't like any of the 3 colors you have chosen with it. I would use marbles, or some muted version of the colors in the stripes. Of course, a lot depends on the block design you are chosing. But that green just doesn't make it for me.