Button1.BackColor = &H8000& works ok, but if I make a loop like this

for I = I to 10
if <argument true then
("Button" & cstr(I)).BackColor = &H8000
end if
next

I get this error: Expected : Linenumber or Label or statement or end of statement
how should I call my Button
I tried with:
sheets("sheet1"). ("Button" & cstr(I)).BackColor = &H8000
sheet1. ("Button" & cstr(I)).BackColor = &H8000
activesheet. ("Button" & cstr(I)).BackColor = &H8000
.... and a lot of others