The journal is printed in black-and-white. Therefore, we prefer that you supply your figures in greyscale.
Figures supplied in colour will be converted to greyscale for print unless the author confirms they will cover the cost of printing in colour (costs available from the production/editorial office).
You may however request for any/all figures to be shown in colour in the HTML (web) version of your article, but bear in mind that the PDF/print version will still be black-and-white, so please make sure that colour is not critical to understanding any figures; and do not describe elements of the figure in terms of their colours.
For example line graphs with several data series can usually be represented adequately in black-and-white by using different line styles and/or different shaped nodes.