We see parent product thumbnail in cart by default. Actually this can be configured. Go to Configuration > Sales > Checkout > Configurable Product Image , and set “Parent Product Thumbnail” to be “Product Thumbnail Itself”. Save it and flush cache. 
We see parent product thumbnail in cart by default. Actually this can be configured. Go to Configuration > Sales > Checkout > Configurable Product Image , and set “Parent Product Thumbnail” to be “Product Thumbnail Itself”. Save it and flush cache.