To add to your suggestions: avoid referring to colors on a chart by name. While it may be able to identify the difference between two colors (e.g. by intensity), it may not be possible to identify the color. In my case, identifying blue and purple are frequently difficult. Presumably this is because purple is a mixture of blue and red.
The issue isn't with referring to colors on a chart by name but with using a color name as the sole identifier. Referring to parts of a chart by color is fine, and provides additional information, as long as a line style or shape identifier is also used, e.g., the "blue solid line" and the "orange dashed line" in the case of a line plot or the "blue circles" and the "orange squares" in the case of a scatter plot. Ideally, I think color swatches should also be included when referring to colors, so it isn't necessary to match the name to the color [1].
Yes, using multiple identifiers would work as well.
The use of colour swatches is interesting, though I would add that it should use a standard palette of colours to ensure that there is also differentiation based upon intensity (which would also help in the grey scale printout example).
