I have a list of values for some data recorded via Magnetic susceptibility, I have these in a shapefile and want to try creating a colour map out of the values. The values that I'm using relate to, OSGB 1936 / British National Grid, EPSG:27700
QGis should be able to import this directly as an XYZ grid (under Raster) provided it meets the following (from the GDAL Manual):
Those datasets are ASCII files with (at least) 3 columns, each line containing the X and Y coordinates of the center of the cell and the value of the cell.
The spacing between each cell must be constant and no missing value is supported. Cells with same Y coordinates must be placed on consecutive lines. For a same Y coordinate value, the lines in the dataset must be organized by increasing X values. The value of the Y coordinate can increase or decrease however. The supported column separators are space, comma, semicolon and tabulations.
The manual also suggests that you name the columns X, Y & Z for best detection but it might work as you currently have it.
Once imported it will need to be coloured in as with any other raster -> properties->Style.