But when I do this, I get 'fill color' option for ALT + H + H (for first H it is going to home and second H it is going to 'fill color' as it is mentioned in the ribbon)
And for ALT + H + U, functions open up for me (under editing)
If you press the Alt key you will see the first combination keys as letters in a black square, look for the one you want, press that letter and then you will see the second letter to press, some times there are further letters to press depending on what you are wanting.
Takes longer to read than do but when you get used to the combinations all that time going from mouse to keyboard will be dramatically cut.
This is for Excel 2010, older versions of Excel may have different key combinations but pressing the Alt key will show you the way to go