Opt+Delete not working on Mac

[pandeyg2106]

I have created a new Alpha channel, and trying to set its foregrounf color to 50% gray. After selecting the 50%gray when I press OPT+Delete to set the foreground color it doesn't work. 
Can someone please help me resolve this? 

Note: My Mac keyboard doesn't have a delete button, and I am using a Logi keyboartd with a delete key.

[c.pfaffenbichler]

Does shift-delete work to raise the Fill-dialog? 

In any case I would recommend creating an Action and assigning a shortcut to that if the keyboard itself might cause communication-problems.