When searching for inspiration I often turn to materials and processes to spark ideas. I keep a sample book of all the different dyes I've encountered so far. Dyes interact differently with different materials, the coarsest natural fibres tend to take colour best, for example hessian. Madder comes as a root which needs to be ground with a pestle and mortar before being soaked in water; warming the mixture will speed up the dye process.
Adding vinegar to the madder gives and exquisite rich saffron colour. When sharing a dye bath with others it's essential to tye a lable with your name to your fabric, to prevent debate about who's piece is whos!
Weld gives a good green colour - the hardest colour to acheive with natural dyes.
Indigo is rare in that it does not need a mordant to be colour fast. The indigo solution can be made up to be dark or lighter.
Logwood is not native to the UK but does give rich violet colour.
Sappan can also give a delicate peach colour when used with specific mordants.