Light and color respond differently outdoors than indoors. Light bounces around, reflects, absorbs, etc;
A trick I've been learning when painting outdoors is to judge an area of color by staring at adjacent areas and sensing the nearby color peripherally.
Stare at the lit up areas to sense the color in the shadows. Stare at the shadows to sense the color of the lit up areas. Look at the sky to sense the colors of the nearby trees...at the trees to sense the color of the sky.
If you stare for example at a gray circle surrounded by the color red...the gray will take on the appearance of red's complimentary- green. There will be sensed a tinge of green in that gray.
So...it depends. If the clouds are to appear as a part of the whole, and not the main
subject itself...it needs to fit into this whole by taking upon itself the influence of its surrounding colors. I suggest therefore...to get into this habit of judging colors in such a way.
You can usually tell someone that copies photographs, because chemically film emulstion does not record this phenomena, and such artists miss this effect.
Clouds will be affected as three-dimensional objects, showing the results of the part hit by sunlight, others in shadow...and do be sure to create good atmospheric effect by playing the cloud's shadow upon the earth below.