This paper and also the one more looking like sandpaper, comes in different colours. It is to make for example the colour white and yellow visible. I assume that the reason the paper is coloured also lays in the fact there will always some pieces of paper be visible. The colour could help in this way lift the painting.
Why this structure of paper? To hold the pastel (crayons) better, to avoid all the dust the crayons produce, to be able to add more layers (different tricks are used to also make this possible with normal paper like spraying with fixation or hairspray after each layer, working with thinner layers is also an option).

Can be that if one works with this paper, little parts should be showed for a special effect. I don't know yet.

I just checked the watercolour paper (190 he) pad and acrylic paper pad I received as a gift. Even the water colour paper has more structure, the acrylic (300 gr) way more. It can be noticed + felt.

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The upper white is meant for acrylic, the one at the bottom is for watercolour paint.

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And here you have at the bottom bamboo paper. It is way cheaper and 250 grams which means also thicker then the green, which is 160 gr.

As you can see it will be hard to use white on white paper. If it comes to watercolour they would leave the white spots unpainted! So white is the colour of the paper. I can do the same with soft pastels and once finished always paints those spots that are left unpainted, or exhange the white for a different colour or use white in the last layer.

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