Rendering item in an ISTER renders them dark in inventory

[Kauruck]

So I am trying to render an Item (eg. an IronPickaxe) with an ISTER. Currently I am using the following code:

matrixStack.push();
matrixStack.translate(0.5D, 0.5D, 0.5D);
ItemRenderer itemRenderer = Minecraft.getInstance().getItemRenderer();
itemRenderer.renderItem(baseItem, transformType, combinedLight, combinedOverlay, matrixStack, buffer);
matrixStack.pop();

where baseItem can be any Item (eg.  an IronPickaxe).

 

The item is rendered fine, except for the Inventory where it appears to be darkend.