Hi Spike - those are the object's edge curves - they're one of the pieces that a model is constructed out of.

Normally the color of the edges is controlled by the style that they are assigned to, so if you select that object and assign a style to it, the object will be colored by that style including all of its edges as well.

So that's one way to change their color. There is also an option to override that behavior and instead make all edges have a specific color of your choice, that's a setting under Options > View > Edge color:



Change that setting to "Fixed color", and then a color swatch will appear next to it and you can click on it to set the color you want.

- Michael