Can I color wood filler by mixing paint or stain into it? Or there better options? – Tip Moses
Rob Johnstone: The answer is yes and no. You can color wood filler if you use the correct product. Wood fillers can have different solvents in them, and the product you use to change the color must be compatible with that solvent. There is a product called, cleverly, Universal Tint, made by a company called Mixol®, that can actually color almost anything. You can also use some aniline dye in both water-based fillers and those with other solvents. I would not use paint- or oil-based stains to color the wood filler, but they might work if the solvents are compatible. There are just better products out there for this task.
Tim Inman: Yes, of course you can color wood with paint in the filler. As always, test the mix for suitability for your purposes! But, paint is paint — a mix of color pigments and sometimes dyes plus bonding agents and film-forming materials. While it will work, it is probably not the best first choice. There is a product family called Universal Tinting Pigments or sometimes Colorants (UTP or UTC in the trades), which are very finely ground pigments in a vehicle carrier which will mix with both water-based and oil-based materials. This would be my first choice for pigment sources. Another good choice in small quantities is tube colors. Acrylic or oil-based tubes of color are available at just about every hobby and art supply store in the world. These are a reliable and high quality source of excellent pigments.