Pico Pixel 0.6.5 will have a grid to isolate individual texels in textures. The grid can be turned on and off and only shows up once texels reach a size of 5x5 pixels on screen.
Rather than a grid made of straight lines going from top to bottom and from left to right, the grid places two small crossing lines (at 90 degrees) at the the corners of texels. The result is rather neat.
OpenGL extension GL_ARB_draw_instanced is used to optimize the rendering of the grid.