Here is the break down from the help file.
Specifies the fading intensity value of externally referenced drawings. ( system variable)
This option only affects the display on the screen. It does not affect plotting or plot preview. The system variable defines the fade percentage of the DWG xrefs. The valid range is an integer between -90 and 90. The fading value is limited to 90 percent to avoid confusion with layers that are turned off or frozen.
0 Locked layers are not faded
>0 When the value is positive, controls the percent of fading up to 90 percent
<0 When the value is negative, locked layers are not faded, but the value is saved for switching to that value by changing the sign
When XDWGFADECTL is set to a negative value, the Xref Fading feature is not turned on, but the setting is stored.
- In-place Edit and Annotative Representations
- Specifies the fading intensity value for objects during in-place reference editing. Objects that are not being edited are displayed at a lesser intensity. ( system variable)
- With in-place reference editing, you can edit a block reference or external reference from within the current drawing. The valid range is 0 through 90 percent. The default setting is 50 percent.
- Controls the amount of fading for objects on locked layers.
- Fades the objects on locked layers to contrast them with objects on unlocked layers and reduces the visual complexity of a drawing. Objects on locked layers are still visible for reference and for object snapping.
Hope this helps.