Detecting wool in a commandblock

When you try to detect wool using detect (after execute) in a repeating command block, the next command is not run.

the command I used was this:
/execute @a ~ ~ ~ detect ~ ~-1 ~ wool 1 /summon Cow

when putting this in a repeating command block, no cows are summoned while standing on orange wool, but when the command is run in chat, a cow appears if you are standing on white wool.