Produces a list of colours that controls the geoms in the plot
ptd_spc_colours(
common_cause = "#a6a6a6",
special_cause_improvement = "#00b0f0",
special_cause_neutral = "#490092",
special_cause_concern = "#e46c0a",
value_line = "#a6a6a6",
mean_line = "#000000",
lpl = "#a6a6a6",
upl = "#a6a6a6",
target = "#de1b1b",
trajectory = "#490092"
)
the colour of the points
the colour of the line joining the points
the colour of the "mean" (average) line
the colour the the lower and upper process limit lines
the colour of the target line
the colour of the trajectory line
A list of colours