All clear glass is transparent but there is a difference between 'Clear Float Glass' and 'Starfire Glass' which is more expensive.

The standard Clear Float glass has a higher proportion of Iron oxide in its raw materials and this can be seen by looking into the edge of the glass. It is evidenced by a green tinge in the glass. The thicker the glass, the more noticable the green colour. If this type of glass is back-painted with a light colour, the inherrent colour in the glass will slightly alter the colour when viewed from the front.

Starfire (Low Iron) glass has a lower proportion of Iron oxide in its raw materials and gives a much better colour match when back-painted.

The colour difference is not so noticable when darker colours are used for the back-painting.

Both splashbacks in the pictures below are backpainted with White. The left image is quite greenish compared with the right image.