[tssva]

What you described is graphics mode 1 or standard graphics. The TI 99/4a also had a mode 2 or bitmap mode. In this mode the screen was divided into thirds each being assigned their own character pattern and color table. This allowed you to change each pixel on the screen individually.

There was still a color restriction. Each row of a character could only contain 2 colors, so every horizontal grouping of 8 pixels could only be one of two colors assigned to that row in the character. This is still an improvement over standard mode which required all pixels of an 8x8 pixel grid defined by a character to be one of two colors assigned to that character.

[ams6110]

IIRC you needed the MiniMemory cartridge and the assembler program it came with (on cassette tape) to access this mode as a programmer.