White is the most commonly used colour in oil painting from the earliest stages through to finishing touches and highlighting. However not all whites are the same. Understanding how they perform helps the artist to choose the right white for the painting in progress.
Here are the most common ranges of white. Although some factory offer more specific types.

Titanium White: The most popular modern white. It is the whitest, and the most opaque bright white with exceptional covering power for strong highlights. It can also be used for mixing and is a good all purpose white.

Zinc White: Less opaque slower drying white, used in the later stages of a painting for subtle highlighting, glazing and blending with other colours to create pale tints. It has a blue undertone.

Iridescent White: A mica based pigment which makes a pearlescent white. It is effective when mixed with transparent colours, and used over dark underpainting.

Underpainting White (fast drying): A titanium pigment ground in linseed oil which is recommended for underpainting or extensive layering with white. It dries quickly to a flat, matt, toothy finish. Specially formulated to resist cracking and shrinking in the early stages of painting.

Flake White (The Old Masters White): Based on lead pigment, suitable for all stages of a painting. It's a high performance milky white, noted for its opacity and durable paint film. When mixed with other colours it creates pure clean tints with minimum loss of tonal value. A titanium based formulation which avoids the hazardous lead based Flake White No. 1. It has a lower tinting strength than Titanium White to match Flake White and a similar drying rate to the original. Classified as toxic according to EC legislation and available only in tins for EC countries.