Hi Gary!

I would stay away from the watercolor altogether - gum-Arabic is used for the binder in it. You need pigment and water only!

Anyway sinopia sells the variety of malachite greens, the price bites though!

My advice would be - get the historic fresco palette select about 10 colours to cover the spectrum - that should be enough for any shade you can possibly use especially at the beginning of the "fresco adventure". Get them in the quantity (for the best price) that should last you for some time. Grind those with the distilled water and store in glass jars with leads under the layer of water (pigment will settle at the bottom as a paste)
90% of the yellow on the ceiling of the Sistine Chapel is painted with just yellow ochre.
Classic oil palette contains only three colors - one yellow, one red, one blue, others (umbers, ochres and such were not even conceded colours - raw umber, burned umber, bone black, white, yellow ochre, red oxide (sienna). Greens were obtained by mixing of the blue and yellow.
However for the fresco painting you need "greens" because of their mineral structure - on microscopic level particles of the most of earth pigment are round and mixing them together results in warm "earthy" tones. Greens and blues at times need
to have "cold" luminosity and particles of the fine ground minerals (stones) such as malachite or lapis lasuly are sharp shaped and reflect light differently than the round ones. For the oil painting it is not important since pigments are suspended in the medium as oppose to be "trapped" inside of the lime crystal.
The rest of the colours are just the shades, the more you have the more you will get confused while painting.

Not to get confused is at most importance while painting fresco, since you have to recreate the tones for the next giornata.

Ilia