For recent some recent publications I designed some figures which rely heavily on different colors to distinguish different features of those figures, or to add more relevant data to the figure. To increase the readability and visibility I try to choose colors which are as far away as possible from each other (i.e. orange/blue, for example).
This approach works fine for colored publications, but I got feedback from readers that it is difficult to distinguish those features when printing the publication in grayscale. To reduce such issues it was suggested to use different line styles (i.e. dashed/dotted/mixed/etc.). This can work for some figures, but for others (where having a continuous line is important) it does not.
Thus, another question came up: How important is it today to limit the figures to be grayscale-friendly? Based on my knowledge, at least, most of the publications are read in a digital form anyway, where colors are used. If not, at least I for myself print all publications in color, to avoid similar issues when reading the paper version.
Therefore, how important is it to keep the figures grayscale-friendly? A similar question was asked here: Why is colour use in academic writing disapproved?, but (as far as I can see) it is more focused on the content of the document itself, not on the figures.