I don't know if grainy is the right word, more like it has a texture. Maybe try starting with brigter colors? The blue and red are quite dark, possibly because the black is showing through?
Every day you may make progress. Every step may be fruitful. Yet there will stretch out before you an ever-lengthening, ever-ascending, ever-improving path. You know you will never get to the end of the journey. But this, so far from discouraging, only adds to the joy and glory of the climb. - Churchill