kono akusentowooru no kabegami ha siro ppoi.

Because アクセントウォール is a loanword based on English accent wall. In Japanese, foreign loanwords are usually written in katakana.

A native-sounding translation idea is:

• accent wall
• feature wall

So this is normal Japanese interior-design vocabulary, even though it comes from English.

この modifies アクセントウォール.

So the structure is:

• この アクセントウォール = this accent wall
• このアクセントウォール の 壁紙 = the wallpaper of/on this accent wall

If you wanted this wallpaper, you would normally say この壁紙 instead.

の links two nouns. It often works like of, but in natural English the relationship can be translated in different ways.

Here:

• アクセントウォールの壁紙 literally = the accent wall’s wallpaper
• more natural English = the wallpaper on the accent wall

So の is showing that 壁紙 is associated with アクセントウォール.

No.

• 壁 = wall
• 壁紙 = wallpaper

So this sentence is not describing the wall itself directly. It is describing the wallpaper on that wall.

Also, 壁紙 is read かべがみ.

は marks the topic.

The topic of the sentence is the whole phrase:

• このアクセントウォールの壁紙は = as for the wallpaper on this accent wall...

Then the sentence says something about that topic:

• 白っぽい = it is whitish / kind of white

So は is very natural here because the speaker is introducing what they want to comment on.

白っぽい means something like:

• whitish
• kind of white
• somewhat white
• white-looking

It is softer and less exact than 白い.

Compare:

• 白い = clearly white
• 白っぽい = looks fairly white, has a white-ish tone, but maybe not pure white

So if the wallpaper is off-white, pale, or only somewhat white in appearance, 白っぽい is a good choice.

Because っぽい attaches to the stem, not to the full -い adjective form.

For 白い:

• dictionary form: 白い
• stem: 白
• stem + っぽい = 白っぽい

This is the normal pattern.

Similar examples:

• 子どもっぽい = childish
• 油っぽい = oily/greasy
• 忘れっぽい = forgetful

So 白いっぽい would not be the standard form.

Yes. Once っぽい is attached, the whole word behaves like an -i adjective.

So you can conjugate it like this:

• 白っぽい = whitish
• 白っぽくない = not whitish
• 白っぽかった = was whitish
• 白っぽくて = being whitish / and whitish

That is why it can end the sentence by itself in plain style.

This sentence is in plain style:

• 白っぽい。

A polite version would be:

• 白っぽいです。

Both are grammatically fine. The version without です is just less polite and more casual/plain.

No. Standard Japanese normally does not use spaces between words.

This sentence would usually be written as:

• このアクセントウォールの壁紙は白っぽい。

The spaces in your example are probably there only to help learners see the parts more clearly.