|Bob Bob Bob|
Not first party but Spheres of Power has the Gleam Brush, which is 200 gp and basically does this but with a paintbrush instead of a pen.
A gleam brush takes the form of a handheld brush with a wooden handle decorated with colored whorls and spirals. This magic brush is considered a masterwork tool for appropriate Craft skills (such as calligraphy or painting) and creates ink of any color, changing to any color the user imagines as a free action; the ink glows, increasing the light level by one step 5 feet around it. The ink created by a gleam brush is nonmagical and permanent, and may cleaned up or removed from surfaces as normal ink can. A gleam brush never runs out of ink. Different styles of brush can be found and produced, ranging from fine tipped ink brushes to wide, thick paintbrushes, but they are always small enough to be held in one hand.
It's probably underpriced since the light effect is basically infinite free permanent heatless candles but you could always remove that if you think it's too much.Personally, I think it's a great thematic fun item and the price is fine. The "but" here is that if the player really wants there's nothing stopping them from painting literally everything glowing neon and decorating your world in cyberpunk.