The thickness of the stem should be slightly thicker than the grass. Add leaves or thorns to the stems to make the flowers look more realistic.
Paint the petals in their base color and use other shades to create highlights, shadows, and details.
Realistic-looking petals would have thin, almost translucent edges. Another optional step is to use a light blue colored oil pastel and lightly shade in a sky, then blend. Add a sun if you’d like.