Hi,
The point of having a main product and then variants is that you can configure stuff in your main product that will be passed on automatically to the variants.
So for example, when you have a 100 variants with the same product image, instead of setting the image 100 times, you do it once in the main product and the system passes the image to all the variants automatically. And it's basically the same for all the product fields. That actually saves a lot of duplication work.
So in your example, if you want to enter a product description you can specify it only for the main product, and not duplicate it for each variant:
product_parent_id;product_code;Colour;product_description
;1501;BLACK;my description
1501;1502;BROWN;
1501;1503;LIGHT GREY;
1501;1504;BLACK;