White's pumping by instants is usually +2/+2 or smaller, but it most often will grant an ability as well. The one exception for white is that it can get larger pumps if the effect is restricted to blockers.
All colors have access to Auras that grant +N/+N. Blue usually doesn't do much more than +1/+1.
Black is primary in straightforward pumping by activation costs on creatures. This is mostly seen on Shades and usually requires black mana. Black will occasionally get smaller buffs by instants, usually with an ability added.
Red has several cheap Auras that give +2/+2 and usually a drawback, though sometimes a small bonus. Red's instants don't usually give toughness boosts but recently there have been instants that target attacking creatures and provide a +2/+2 or +3/+3 boost. Infuriate is an outlier, being usable on defense; Brute Force is a Planar Chaos bend; while Integrity is a hybrid mana bend. Inordinate Rage shows that the effect is becoming more mainstream.
Green is secondary in straightforward pumping by activation costs on creatures. These often are unlimited but usually only when the activation cost is high enough that multiple activations don't happen until the late game. Green is primary in one-off pumping, the almost exclusive Rootwalla-ability. The most common use of pumping by instants is Giant Growth–like effects, usually +3/+3 but it can vary a little. Smaller pumps are used with fight spells, letting smaller creatures fight on-curve more often. Green is the one color that regularly grants +3/+3 and above on auras.
This ability, as a repeatable activation, is what referred to as "firebreathing." It's primarily seen on red creatures. White tends to get one-time upgrades of usually +1/+0, potentially to the whole team. Green gets +N/+0 when it's not intended for it to survive the fight.
Black and red are the two colors that tend to pump power as a spell without also pumping toughness. To make them useful in combat, Black either regenerates, grants indestructible, or something similar, while Red grants first or double strike. White does it occasionally as a combat trick but usually never more than +2/+0; both white and red share the "Trumpet Blast" effect, with white granting toughness higher costs.
Red is the color most often to have just power-pumping Auras (including "firebreathing" Auras). White and black do it occasionally with white tending to go no higher than +2/+0. Blue and green do it on rare occasion with blue, like white, sticking at +2/+0 or lower.
As this is mostly used as a kill spell, the ability resides mostly in black.
These tend to be flavored as "push your luck" cards that can double as creature kill. Black will go up to -3 on the toughness, whereas red tends to stop at -2. Blue will do a "make me a shapeshifter" flavored Aura from time to time.
This is also used in blue on Elementals and Shapeshifters, often on the same cards with the +N/-N. White, on rare occasion, will have an activation that uses this defensively. Largely phased out as seen on the +0/+N paragraph; few instants or Auras perform this effect nowadays.
Almost entirely relegated as black creature removal, few creatures inflict this on themselves. Black gets this in many forms; some are small or inefficient enough to act as combat tricks, but others are large enough to count as direct kill spells.
In blue, this is shrinking its target. Instants typically are paired with some form of scry effect or cantrip due to the low impact; blue Auras are quasi-removal effects, with all the downsides attached.
In black it's usually some form of torture. With all its creature interaction, it tends to not need it as a spell or aura. Some creatures give themselves -N/-0 in exchange for some form of evasion.
White used to do this quite a bit, but R&D has backed off because it tends to just clog up the board. It is now used to enable small-creature attackers by invalidating low-power blockers. Green also uses this on occasion with the same design intent, and some number of reach-granting instants give no power, and finally one fight card gives only toughness rather than also power (Warbriar Blessing). Blue uses it, sometimes with hexproof, on protective spells.
White is the color most likely to pump its team, most often with +1/+1, but it will occasionally go up to +2/+2. Green's team pump starts at +3/+3 and often also adds trample. Team pump that only pumps power is most often done in red, usually affecting attacking creatures. White will sometimes pump its team's power without pumping toughness (although it more often pumps both).