Combine: Previous Calculated Cycle Color Value 
Texel0: Point Color at current mipmap level 
Texel1: Point Color at next mipmap level 
Primitive: A Colour Register held by the Combiner for Colouring textures on a Realtime lit Primitive
Shade: Vertex Color 
Combined_Alpha: Previous Calculated Cycle Alpha Value 
Texel0_Alpha: Point Alpha at current mipmap level 
Texel1_Alpha: Point Alpha at next mipmap level 
Primitive_A: Primitive Colour Register Alpha component
Shade_Alpha: Vertex Alpha 
Env_Alpha: A Colour Register held by the Combiner.
LOD_FRACTION: An Automatically generated Float (0.0-7.0) to indicate Mip-map Level +1 AND change(x.0 - x.99)
Prim_LOD_Frac: A Manually Adjustable LOD_Fraction Multiplier to either hasten or delay the next Mip-Map Level. 
K4: YUV-RGB Conversion Constant 
K5: YUV-RGB Conversion Constant


Refer to http://fgfc.ddns.net/NINTENDO 64 SDK 5 _CDROM/man/allman50/pro-man/pro12/12-06.htm#02
12.6.2 CC Internal Color Registers 

There are two internal color registers in the CC: primitive and environment color. The primitive color can be used to set a constant polygon face color. The environment color can be used to represent the ambient color of the environment. Both can be used as source for linear interpolation. The names "primitive" and "environment" are purely arbitrary; you can use them for any purpose you wish. 

Table 12-21 gsDPSetPrimColor(minlevel,frac,r,g,b,a), gsDPSetEnvColor(r,g,b,a) Parameter Values 
	minlevel 	minimum LOD level 
	frac 		LOD fraction for blending two texture tiles 
	r,g,b,a 	color 


haha ok, this is good, I actually made a mistake above which I have now corrected.
this :- 
	A Manually Adjustable LOD_Fraction Multiplier to either delay or hasten the next Mip-Map Level. 
	Generally Used in Detail Maps to prevent Full Exposure of Level 0 by clamping to 0.8.

was slightly wrong in that I counted 2 parts as 1.
MINLEVEL is used to clamp level 0 to 0.8