Hi WF, there are many different variables in dyeing. The first is water quality. If in doubt, use distilled water as it's pure and contains no minerals or additives in the way tap water does. The addition of minerals etc can affect your shades depending on what you're dyeing. Next is 'uptake'. Due to the molecular size of the dye particles some colours will be absorbed faster than others, so you'll need to leave things be until
all the colour has been absorbed. This is especially true with mixed colours, ie, colours that are a mix of red, yellow, blue etc. Dyeing one colour on top of another will often have different effects depending on which colour you dye first. For instance, dyeing chartreuse over yellow will have a different effect than dyeing yellow over chartreuse. Sometimes you'll want to dye a dark base colour and then 'blast' it out with a lighter colour to achieve a certain shade by reflected light with a different shade by transmitted light.
As far a secret recipes go... well... they're secret.
Anyway, experimentation's half the fun.
Quick edit.
Never use aluminium pans. The acetic acid and heat creates aluminium salts which will dull your colours.