Starting from the Black undercoat and using the limited palate I have decided on in other posts.
I hope to do a pattern close to a Tesler tower with sparks climbing cross ways up the length of the blade towards the tip. The edges will be bright but brightest where the sparks hit the edge.
This is the same method some folks used to use on Gemstones, comming up from black to light.

1) Start with Spacewolves Grey and line those points and edges where the power sparks will be brightest. Include the cross ways sparks.

2) Thin Blood Red to watery. Add it in many thin layers concentrating on the areas around the Spacewolves grey area. I am seeking a 'Gausian Blur' look. Continue at least until the Spacewolves Grey lines cannot be discerned.

3) Thin Sunburst Yellow to watery. Mix a little of this with the watery Blood Red to get an orange. Using this, add highlights on the powersparks and edges where the sparks hit the edge.

4) Mix a little of more of the Thin Sunburst Yellow with the watery Blood Red to get a brighter orange. Using this, add smaller highlights on the powersparks and edges where the sparks hit the edge. This is where I stopped.

All over the planet Tau Firewarriors scrambled from their barracks to defend thier installations from the Eldar Exodites, with whom they had been friends for so long. As they now understood it, their Human trade partner had been attacked without reason in the wilds. Worse still, the Eldar had tracked the happless human back to the Trade Enclave in the principal city, and made a brutal thrust into the heart of the city to get at him. Many Tau of all castes had died. Now they must be vigilent, defending their posts long enough for the Ethereals to organise the defence.
The attack, when it came, was not from the direction of the wilds as they expected, but from the city behind them.
As the Sword of Vashar fought pitched battles with Exorcists Marines in the streets of the Trade Enclave, the IX Company, 291st Death Korps had emerged from the hold of the bulk trader the Inquisitor had arrived in.
Before the rest of the Division could land the Tau orbital defense ordinatus needed to be put out of action. Marines may be able to weather the storm of fire from the Defensive batteries, but the Divisions landing craft could not.
Wasting no time, Colonel Paulus sent strike teams into the surrounding plains to seek and destroy Tau orbital defence facitlities.
The first contact with the Tau occured when elements of IX Company met the Tau in a valley leading up to a command bunker of the planetary defence batteries on the outskirts of the Principle city. A IX Company column of Grenadiers in Chimeras, stumbled into a Tau patrol. After the inital shock, who knew the Humans had such forces on the Planet, the suprised Tau quickly recovered their composture. Imperial chimeras fell easy prey to the Tau guns and before long the valley was littered with burning vehicles.

The Secret was now out, word flashed around the Fire-warrior command net, not only were the Eldar Exodites turning against them, but the very Humans they were trying to protect had stabbed them in the back. Before long the stiuation for the Tau of H'Rus was to be come much worse.