What colour is this pain?

I don't know about the color of 'pain', but this gesso is white.

So is it clear or white? I'm reading reviewers saying two different things.

If you are looking for a clear gesso, make sure the product says clear....I use a golden clear gesso. The gesso does look white, goes on white, but dries clear. It made me nervous the first time....but it does dry clear. Basic gesso looks white, goes on white, and dries white.

Can this be used as a base coat for model horses/figurines?

If your item is plastic, I would just use the paint that is recommended for plastic models. I can't see why you would need a base coat of gesso. Gesso is a rather thick solution made of glue, whiting and linseed oil (usually). It is used for porous backgrounds to seal and somewhat fill any small roughness. Then it should be sanded. It works great for cloth, canvas paper mache, dip & drape type products. For plastic, I just use plastic model paint.

Can this be used as a base gesso for oil painting on canvas ?

Gesso is used to prep canvases for painting with either oils or acrylics. You can paint oils over acrylics but never acrylic over oils. I hope that answers the question