I'm going to try and give you an idea of the colours/shades that
you can achieve on your hair using a mix of henna / indigo /
cassia.
Please remember that these colours are an estimate. These are
natural dye products so an exact shade cannot be guaranteed.
Experimentation is the key.
Strand tests are highly recommended for both a colour check and
allergy check (though allergies to these natural products are very
rare)
If you use pure henna the following colours will take
effect:
Blonde - Vivid Red
Dark Blonde - Vibrant Red
Red - Vibrant Red
Medium Brown - Auburn
Dark Brown - Dark Auburn
Black - Black with Red shimmer
Grey - Coppery Red
If you use 1/2 indigo and 1/2 henna, the following
colours will take effect:
Blonde - Medium Brown
Dark Blonde - Medium Brown
Red - Medium Brown
Medium Brown - Medium Brown
Dark Brown - Warm Brown
Black - Warm Black
Grey - Dark Brown with Reddish Highlights
Using pure cassia will make your hair glossy - whatever your
original colour but has been known to add a slightly yellow tinge
(strand test first).
If you use 1/2 henna and 1/2 cassia, you hair will
take on the reddish tones of the henna but softened by the cassia,
will not be as vibrant.
Changing the proportions will change the shade - the more indigo
you use the darker the shade. Therefore 1/3 henna and 2/3 indigo
will be a much darker shade of brown on most hair types, than say
2/3 henna and 1/3 indigo which will go redder.