ConstExcel's Fill Effects offers exactly two colors, six shading styles and three variants of each — a fixed menu because its file format is all it can express. This authors the model directly instead: any number of stops at any offset, linear at any angle or radial. Everything it produces still round-trips (a two-stop linear gradient is what Excel's grid writes); the extra reach simply is not reachable from Excel's own dialog.
The gradient editor behind the Fill tab's Gradient mode.