This is the 11672nd most frequent Spanish word.
fundirse
To melt, merge, or fuse.
Here 'fundirse' refers to the physical melting of the ice due to heat.
Cuando hizo mucho calor, el hielo comenzó a fundirse.
When it got very hot, the ice began to melt.
Here 'fundirse' is used in a metaphorical sense to describe the blending of colors.
En ese momento emocionante, los colores del cielo parecían fundirse en uno.
In that thrilling moment, the colors of the sky seemed to merge into one.
Here 'fundirse' metaphorically represents becoming one or deeply connecting with something.