80 PALETTE FORMAT 255
 90 BANK 5 ERASE 0,6912,255
100 %l=6144
110 REPEAT: WHILE %l<6912
120 IF %c>255 THEN %c=0
130 BANK 5 POKE %l,%c
140 %l,%c+=%1
160 REPEAT UNTIL 0
170 PAUSE 0

Don't worry about the unknown commands yet. What the program does is to create an 8-bit palette for Layer 1,1, then enable the EnhancedULA and switch it to Full Ink Mode then cycle through all 256 colours of that palette by writing in the COLOUR_FILE area the specific attribute. We'll go into more detail on how that works when we examine IN and OUT and the ZX Spectrum Next Ports System in Chapter 22

Palette-based hybrid linear bitmapped colour display

This system of colour organisation, storage and display is applicable to Layer 1,0, Layer 2, Layer 3 and partly applicable to the Sprite System. Before we explain why it's hybrid, we'll point you back to the beginning of this chapter and especially the Colour organisation and representation section. As you recall, we said there that the ZX Spectrum Next can handle both 9-bit and 8-bit colour. This is technically inaccurate as we have a broader spectrum of colours that a single byte can display.

We'll take a small detour here and explain the concept of a palette. A palette is a subset of colours where each colour displayed on screen, is not actually stored as the colour component information it's made up of, but rather as a pointer (or index) of the actual colour that's stored somewhere else. This subset in the ZX Spectrum Next's case is comprised of either 256 pointers (therefore we require only an 8-bit number to store each pointer) or 16 pointers plus one offset (therefore we require only a 4-bit number to store each pointer with an additional 4-bit number to point us to one of 16 groups of colours) to the actual colours which are represented by 16-bit numbers (therefore a set of two 8-bit consecutive numbers which have 6 bits⁵ unused, give the 9 bits of the actual colour stored, albeit rather inefficiently).

There are 8 palettes in the ZX Spectrum Next. Two for each graphics system:

• Layers 0 and 1 use two
• Layer 2 uses two more
• Layer 3 also uses two –and–
• The Sprite System uses the last two

With two palettes, all 512 possible colours of the ZX Spectrum Next can be recalled, rearranged and stored and therefore assigned to pixels, character tiles or attribute cells according to the layer in use, on screen. That doesn't mean all can be displayed simultaneously without some clever NextBASIC tricks. Normally only 256 can be shown on a particular layer at one time.

The ZX Spectrum Next palette system has a special mode where if one were to use an 8-bit colour in the R3G3B2 format and assign one palette in sequence to the value that equals the pointer value (for example set palette location 15 to be of a value 15) then we could treat the entire display of Layers 2 and Layer 1,0 (LoRes) as 8-bit, treating from then on the display instead of a palette-based one, as a bitmapped one. This is exactly why we can call it hybrid.

⁵ Obviously 16 positions minus 9 positions should equal 7 unused positions, however there's one more bit used called the 'priority bit' which although unused in the case of other layers, is used in Layer 2 palettes as we'll see in the next section.