The colour red does not project very well, especially narrow red lines on a black background. The solution offered here will work in most cases (but not all).
To change the colour of a line on a graph, right click somewhere inside the graph and select ‘show’ and then ‘legend’ (some graphs already have the legend showing). A box near the top right hand corner of the graph will appear. Right click inside it, and you will be able to select ‘colour’. A colour palette will appear. Select your preferred colour and it will change the plot accordingly. You can then hide the legend box again by right clicking somewhere inside the graph and selecting ‘show’ and selecting ‘legend’ again. Your change will be a temporary one; it will be lost as soon as you quit the simulation.
Changes of colour may also be advisable in some simulations in order to make things easier for colour blind pupils.
Notice also that right clicking on the legend also offers the possibility of changing the ‘linewidth’. This may be a useful change to visually impaired students or where the projection is particularly poor.