Hi L .....
So you asked about paint - oh boy, you are in for a long response! Hope this is not too much. I'm not sure how much you know about paint so here is perhaps a lot of information but still not nearly everything there is to know about paint. I'm a detail-oriented person so to me these are the basics, haha.
First, a little on the physical properties of paint:
(you probably know a lot of this from the silkscreening, but I'll go over it anyway.)
Pigment load is the ratio of pigment to medium. A medium has no colour and it can be oil, water, acrylic polymer, egg yolk, casein etc. Ok, so egg yolk is yellow of course, but when thinned out it is very transparent. No colour basically means no colour added.
If you are using paint with a low pigment load you will have colour that is less vibrant and more transparent than that of paint with a high pigment load.
There is also some variation of the actual pigments used to make very similar colours. Two colours can look the same optically, but when brushed out onto a surface or mixed with other colours you will see that they behave quite differently. Some pigments are inherently transparent, some opaque. Some have a tendency to dry flat while others dry more glossy.
You can mix mediums with your paint. Basic acrylic medium comes in gloss, semi-gloss or matte. Gel medium will thicken your paint, allowing for impasto effects. Modelling paste medium can be carved into for very textural effects. All the these mediums can be mixed with the paint, or applied under or over the paint layer.
One advantage to applying gloss medium over your paint layer is that you can paint on top. You cannot paint on top of varnish - the paint will not adhere properly and the colours (especially dark colours) will go cloudy over time.
Another advantage is that the medium will seal the surface so that when you apply varnish on top you will have a uniform gloss. Varnish protects your painting because it is non-porous (unlike paints and mediums), and some varnishes have UVLS filters which personally I like.
I use mostly liquid acrylics, because I like to use thin glazes and washes of colour. I tend to make a thin mix of 50/50% water and gloss medium, adding a few drops of Flow Release (golden product) because it does this cool staining thing.
I also like to draw on top of the paint with oil pastels. Then I seal the whole thing with several coats of gloss medium before varnishing. This is what I did with the purple/yellow one.
GOLDEN - intense colours and dry quite shiny. Some of their paints feel very "plastic-y" to me. Liquid and heavy-body acrylics. Huge selection of mediums. Expensive! http://www.goldenpaints.com/
CHROMACOLOUR - colours are often not as intense, consistency a bit like gouache - not plastic-y at all, quite opaque and a velvety finish when dry. Liquid and heavy-body acrylics. Not as expensive as Golden. http://www.chromacolour.com/
STEVENSON - similar to Golden but not quite as shiny. Considered "student quality" by some artists, but I find they have a decently high pigment load. Heavy-body paints only. http://www.dlstevenson.ca/
LIQUITEX - don't use much but very high quality paint. http://www.liquitex.com/
And then a little on technique:
Layering works both ways : light-to-dark, or dark-to-light. You will get different effects depending how you go. If going light-to-dark you will be able to keep a glow in the colour underneath. If you go dark-to-light you will be able to achieve lovely subtle effects in your dark areas. I often work both ways on the same painting, choosing areas for maximum effect.
(I think the yellow/purple layered one is mainly light-to-dark. With the hard-edged "folky pattern" ones I work both ways.)
Sometimes if you want a crisp or intense light colour over darks you can lay white down first, just in the areas where you plan to apply the light colour. Don't worry about making the white totally opaque, it is mainly to supply a lighter area where the light-coloured paint will show up better on top of the darks. If you don't use the white underneath, you will need to either use thick paint* or use several layers of your light colour over dark areas. Either method can give lovely effects.
*the danger of a thick layer of acrylic is that sometimes it will "crack" while drying! This applies to mediums and varnishes as well as paint.
No matter the medium (oil, acrylic, &c), if you start with a white ground you will get maximum intensity of colour. This is one of the reasons that canvas is gesso'd before painting.
There are some specific colour exercises that I could do with you if we were geographically closer! Maybe next time we visit... but that could be some time and meanwhile you want to paint. It might be worth your while to take a colour theory course somewhere. This will teach you a lot more than just mixing colour - it will teach you how paint in fact responds to itself and to various external factors. If you study these things you can experiment more productively.
Whew - I hope that's helpful and not too long-winded!
Please say hello to B and to J, hope you are all well and enjoying life.