I'd miss a feature to set different colors for filament printed by different extruders in the print preview. This way, in the preview of, e.g., a multi-color print one could immediately see which extruder is responsible for which line of filament.
As a work around right now you can apply significantly different speeds for both extruders to check that they are both printing in preview. Just change it once, preview, and change it back.
That said, I don't necessarily want to lose the speed based color. A toggle box between speed based colors and tool based colors would be best.
I would like 3 G-code viewing options: Color By Speed (the currently mode), Color By Extruder, and Color By Process.
I use the speed color scheme a lot to ensure my print will work well before printing. This is very useful as is, and one reason why I purchased Simplify3D.
There are times when I really need to view the g-code to determine exactly which extruder is creating which portion of the object. As processes get complex, it can be hard to keep track of which extruder is doing what. I am currently using FlashPrint to view which extruder is responsible for which part of my print prior to printing. It works well, but it's an additional step I'd rather not have to take.
Being able to set the extruder color would be very useful. FlashPrint doesn't let you set the color. In this view, it would be useful to be able to show/hide different extruders by clicking check boxes associated with the extruder. I envision this check box selection area being where the current print speed color chart is. Instead of the speed chart, there would be a check box for each extruder, it's number, and it's color next to it. Only extruder's who's check box is checked would be visible in the g-code preview.
In the third option, Color By Process, the colors shown are the colors associated with the process that created the g-code. Each process could have it's own color assigned to it. Such a view would make it easy to see what each process is doing in a print job. There are times when this is very useful, especially when attempting to find errors in processes, where one process might be overlapping another. In this view, it would be useful to show/hide processes during viewing, so that you can easily spot overlapping processes. As with the Color By Extruder view, there would be check boxes in place of the current print speed color chart. Each check box will have the process name and color next to it. Only processes who's check box is checked would be visible in the g-code view.
This feature was implemented in version 3.0. You can now color the preview by speed, active toolhead, or feature type. Choose "active toolhead" to see exactly which extruder is printing which part.