Crema should be a deep brown or rust color, if it is not, try some of the suggestions below.
Is it more of a cinnamon color?
Make sure the brew group and boilers are fully heated. Use a less acidic coffee blend.
Is it whitish with brown streaks?
Review your tamping technique; the tamped coffee has fractured or a gap has developed between the coffee and the side of the filter basket.
Is it thin and fast-flowing?
Review your tamping technique; the tamp may not be firm enough to provide an even resistance to the brew water. Try using a finer grind. Also, check the coffee's freshness.
Is it barely dribbling out?
Review your tamping technique; the tamp may be too firm. Try using a coarser grind.