Pipes have the following general appearance properties.
The width of the pipe (in pixels). You can change the width by clicking the up and down arrows to the right of the field, or by entering another value in this field. Every pipe needs to be at least 1 pixel wide.
[Line] Highlight Color
The color of the pipe where it is "in the light"; that is, the brightest color on the pipe.
[Line] Lowlight Color
The color of the pipe where it is "in shadow"; that is, the dullest color on the pipe.
For help on the remaining properties tabs, see Defining Common Object Properties.