recording dates - display format & colour scheme

non-urgent but on hover info gives

date
week (nth in the year)
y = N (no recordings)

could drop the week (meaningless, unless we make it nth week in survey)
and change "y = 1023" to "N Files = 1023"

ALSO

colour scheme has strange scaling. for sounding out y = 1344 is dark green and 1056 is almost invisible is so pale.
Can it be rescaled to white = 0 ?

No file or test is named; start by locating the hover information and the sounding colour-scale entry points in the dashboard. Done means removing or revising the week text, changing the “y = N” label to “N Files = N”, and rescaling the colours so zero is white while preserving useful differences between values.

Written by the indexing model from the issue text.