Blonding is a process, not a point. It indicates the degree of extraction -- under, full or over.
The user should not look for the "blond" point, as much as for the point at which the extraction becomes too blond (extracted) for his tastes and should be stopped. The color of the stream should look different for ristretto, normale and lungo extractions. Knowing what you want goes a long way towards getting it.
Depending on light and angles I usually find it easier to read the top of the pour than the stream.
Drop a nickel in the pot Joe. Takin' it slow. Waiter, waiter, percolator