Have been using the diggers home fiberglass kit for a while now
When using white filler mixed with resin the finished result has an ever slight blue tinge to it.
Is this the resin or is there an additive I can use to match the colour of the boads ie off white to yellow

What other products are good to use?

In my experience, having a blue tinge means that you have not put enough white colouring in. Be warned, the colouring offsets the catalyst (fixer), so you should add a few drops more.

Blending colours via resin is very difficult. Best results are through a surface spray once the ding is filled and sanded.