 Re: It has none.  Should it?  Where on the motherboard would the lights/light effects be located? It should not have the traditional yellow orange light.  Last time I saw those lights on old optiplex 700 series and XPS 700 series which were 10 years older than 8900.  you are correct that modern/recent XPS motherboard has no lights or light effect.  I was thinking of the modern aftermarket gaming boards.  Dell XPS board is oem often made by MSI.
Awhile back, all Dell motherboards had an orange flea LED indicating that 5V stand-by power ("flea power") was available - that is, the system had a power cord plugged into the wall and power was available. I don't see that amber/orange LED on my XPS 8900 desktop's motherboard, which is plugged into a working electrical outlet.  Are those LEDs now history?  Are they no longer on Dell motherboards?
Is the Orange Flea LED/Light on the Motherboard, now History?