https://github.com/ikirill/hl-indent.git
git clone 'git://github.com/ikirill/hl-indent.git'
This modes puts indentation highlights below the starting character of a line on subsequent lines, like this:
some line
| some other line
| | another line
| | | an indented line
| fourth line
final line
This works in every mode, but is more useful in haskell, which doesn't require indentation levels to be at multiples of a specific level.
If the minor mode hl-indent-mode-blocks is on, this mode will
instead highlight blocks of indentation like so (where different
symbols represent different colours):
xxxxxxxxxxxxxx
oooooooooooo
oooooooooooo
*******
*******
**********
oooooooooooo
**********
xxxxxxxxxxxxxx
Enable hl-indent-mode.
There is also hl-indent-mode-blocks, but it is less useful
because of limited color contrast, depending on face settings.

hl-indent-face (which is fringe by
default), and also hl-indent-block-face-1, from 1 to 6.hl-indent-mode puts its highlights, use the
function hl-indent--debug-faces together with either
hl-indent-mode or hl-indent-mode-blocks.