Easy skydome

Make a sphere with a normal modifier ... then make a gradient ramp material with noise. Note the material is set to 100% illumination.

If you mirror instead of tile you can avoid seams [except for nasties at the poles.] You can also rotate the pattern on W if you want.

You can use any colors you want ... work with the noise size ... fractal is nice ... levels brings more detail in the cloud edges ... even gradient type can be interesting.

Finally, right click/properties the sphere and turn off receive and cast shadows: