Melt into
Definition 1 of 3
Pro Tip 1/2Subtle Change
Used when a change happens so slowly it's barely noticeable, often in a natural or artistic context. 
The artist's use of color made the painting's foreground melt into the background seamlessly.
Pro Tip 2/2Visual Imagery
Evokes a vivid picture of one element gradually blending into another. 
In the evening light, the old path seemed to melt into the overgrown field.