This is a demo piece for colour planning, so first of all here is some magic for seeing colours! (b.t.w. I have mixed feelings about working using photos, but that’s a topic for another day. This is rather different.
Take a photo of your subject and use Photoshop to reduce it to about 50 pixels, 72 dpi. It will end up being 2-3cm. Then enlarge it to about 20cm, by uploading it into any programme e.g. Word and pulling on the ‘handles’ not in Photoshop by increasing pixellation. Now it will be very pixelated and you can see exactly what the colours are. Of course as an artist it’s great to exaggerate or change them, but this is a good start. This also roughs out the darks and lights. Look at how the background goes from quite dark on the right to really pale in places on the left. This excercise builds an awareness of tonal change.
Here is the underpainting with Burnt Umber rubbed onto the background, transparent white on the garlic and shadows in Burnt umber mixed with Ultramarine. Below is the final painting with a bit of knife work on the fluttery skins.
And while I am on the subject of garlic, do you know how to separate and peel a whole head of garlic quickly? The Guardian says 30 seconds. This is alchemy. You just shake it up in a jar. Check this link!