Masking allows you to make your aura look like anything else, how effective that is at hiding you is debatable. They make it pretty clear in astral space descriptions that things still generally resemble what they look like in the real world while being made up of cool psychedelic colors and clouds and hazes and such around them, at least for living things. Its why identifying Dragons and shape shifters that have not learned masking can be very easy. When you see (Astrally assessing) the guy walking down the street with a wolf aura the jig is up and you know your looking at a wolf shifter, same thing for a dragon that has shape shifted into a human. Just like a mage that uses the Shape shift or critter form spells can be spotted pretty easily by anyone astrally perceiving because a) you have a spell aura around you and b) you have a human aura not the aura of what ever animal your changed into. Now the Masking meta magic lets you change that, if you shape shift into a dog and use your masking and extended masking to make your aura look like a dogs aura and hide the active spell on you then when some one looks at you astrally if they dont break your masking then they see a nice mundane poochy and react accordingly. Its worth noting that as a street mut in the barrens draws little to no attention unless some one is hungry while the same dog in the middle of a high end corp black lab probably draws just as much attention as if you just walked down the hall in human form because Hey no one has a dog on site and this is not a causal entrance area. Kinda like if I saw a dog in my office, dogs are not supposed to be here and I would take immediate notice and action about it. If you are just altering your aura to be mundane you dont need a bunch of extras because your taking an awakened human aura and making it a mundane human aura so its the same type of aura just with different attributes. Same thing if you boosting or lowering your magic rating, all your doing is taking an awakened aura and adjusting its strength so you appear to have a higher or lower magic attribute ( I kinda always saw this as glowing brighter or dimmer).
So the whole I want to make my aura a plants aura is fine, but unless he does something else to disguise himself its going to be pretty obvious what going on to any astral on lookers because you see a guy with the aura of a plant. Generally some thing like shape change/ critter form or physical mask needs to get involved and then you need extended masking to hide the active spell, I might also let a ghille suite with freshly harvested local greenery work pretty well for a few hours, but keep in mind that you still have the same basic shape and size so hiding in the branches of a tree could work pretty well but being a potted plant in an office building not so much.