<< but the image that I received is not what I excepting, apparently the MacBook uses YPBPR instead of RGB >>
To get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display. "No signal detected" is generated by the DISPLAY, not by the Mac.
This query is only sent at certain times:
• at startup
• at wake from sleep
• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go
• on invoking Option-(Detect Display) button in Displays preferences (from another display)
Dell has a reputation for being quite sloppy about the EDID data their displays send. Since they work mainly in a the PC world, it is not an issue, because the User of the PC sets the display parameters manually.
If your quote above is correct, it is because the Dell is telling your Mac YPBPR is its preferred protocol. Macs do not assume anything about external displays -- they rely on the supplied EDID data from the display. If it is wrong, your picture is wrong as well. This is a DEFECT in the Dell display, that DELL Should fix, but finding a person who knows what you are saying at Dell will be difficult..
Executive summary: To work-around that Dell issue, you may need to install third-party software that allows you to override the settings the Dell display is providing. SwitchResX is one such application. Displays.app is another.
