Favourite album with predominantly BLUE cover art...

[Thorn]

Go.

[Eoin McLove]

Ride the Lightning.
In the Nightside Eclipse.
Wisdom Floats.  (Not exactly a favourite, but a blue oddity. )

[Bürggermeister]

[Mithrandir]

[The Great Cull]

Ride The Lightning
Left Hand Path
Demanufacture

[Eoin McLove]

What's this? Never seen it before.

[Carnage]

Odd question but there's fucking loads I love:

Maiden: Live After Death & Seventh Son Of A Seventh Son
Metallica: Ride The Lightning
FF: Fear Is The Mindkiller & Demanufacture
Godflesh: Selfless, Us And Them & Post Self
Entombed: Left Hand Path
Sepultura: Schizophrenia
Blood Incantation: Hidden History Of The Human Race
My Bloody Valentine: mbv
Mansun: Attack Of The Grey Lantern
WITTR: Black Cascade
Porcupine Tree: Fear Of A Blank Planet
Pig Destroyer: Phantom Limb
Napalm Death: Smear Campaign
Meshuggah: Nothing (Remixed)
Bathory: Nordland I
Devin Townsend: Ocean Machine: Biomech
Nick Cave & The Bad Seeds: Murder Ballads
Dead Can Dance: Spiritchaser
Electric Wizard: s/t
Cathedral: Soul Sacrifice & The Ethereal Mirror
FNM: Angel Dust
Helmet: Meantime
Megadeth: Rust In Peace
Death: Spiritual Healing
JAMC: Darklands
Trouble: The Skull
Kraftwerk: Autobahn

[Carnage]

What's this? Never seen it before.

Masters Of Reality: s/t AKA The Blue Garden, another class one.

[Yung Led Zeppelin]

Stretching it? Maybe

[Eoin McLove]

What's this? Never seen it before.

Master Of Reality: s/t AKA The Blue Garden, another class one.

Never listened to them. Stoner stuff?

Forest of Equilibrium!

[Anvil]

This is possibly the weirdest thread I have seen in ages, but I approve 

First album that came to mind was Saxon's Denim & Leather.

After a little think (which is very hard for me) I would have to say my favourite is...

Iron Maiden - Live After Death
 

[Eoin McLove]

Seventh Son definitely.

[Black Shepherd Carnage]

Haha, love the theme! Will have to double check a few that come to mind but a couple recent ones not mentioned yet:
Stormkeep - Tales of Othertime
Sweven - The Eternal Resonance

[Black Shepherd Carnage]

And speaking of tales:
Amorphis - Tales from the Thousand Lakes

[Carnage]

What's this? Never seen it before.

Master Of Reality: s/t AKA The Blue Garden, another class one.

Never listened to them. Stoner stuff?

Forest of Equilibrium!

Yeah, laid back rock & roll, with sort of a stoner buzz. More '70s influenced than weed fuelled. Main man is Chriss Goss, who produced a lot of the 'desert' scene bands. That album is brilliant, they're hit & miss after. Deep In The Hole, Welcome To The Western Lodge, Flak 'n' Flight & the unreleased album are all great IMO. You might have seen this video back in the day:

https://youtu.be/3zkxklzhAn8