The natural colour of the wood, and any existing coating,
The texture and absorption of the surface,
The way the products are applied.
In order to do this, the coating must contain a pigment/colour, which by nature will alter the appearance of the timber. In addition, clear finishes have less protection for themselves from sunlight, and may become brittle, peel and crack, leading to extra work at redecoration.
To achieve a lighter shade requires either stripping of the existing finish and re-coating, or the application of an opaque, paint-like coating like Sadolin Superdec.