sasiiro ga tuyoi.

It is usually read さしいろ.

• 差し色 = an accent color, meaning a small but noticeable color used to stand out in an outfit, room, design, etc.
• In fashion and design, it often means a color that adds contrast or a visual highlight.

差し色 refers to a color that is added as an accent.

For example:

• mostly neutral clothes + one red bag
• a simple room + one bright cushion
• a plain design + one vivid highlight color

So it is not just color in general. It specifically means a color used to create emphasis or contrast.

が marks 差し色 as the thing being described by 強い.

So the structure is:

• 差し色 = the accent color
• が = subject marker
• 強い = strong / intense / prominent

A natural way to think of it is:

• The accent color is strong.
• The accent color stands out a lot.

In short, が points to what has the quality of being strong.

In Japanese, 強い is often used more broadly than English strong.

With colors, light, flavor, smell, and impressions, 強い can mean:

• intense
• bold
• pronounced
• striking

So 差し色が強い does not necessarily mean the color has physical strength. It means the accent color has a strong visual impact.

Not automatically.

強い itself is neutral. Depending on context, it can be:

• positive: bold, effective, eye-catching
• negative: too loud, too harsh, overpowering

So 差し色が強い can mean something like:

• The accent color really stands out.
• The accent color is quite strong.

Whether that is praise or criticism depends on the speaker’s tone and the situation.

Yes. This is a completely normal Japanese sentence.

Japanese adjectives like 強い can act as the predicate by themselves. So:

• 差し色が強い。

  already means:

• The accent color is strong.

You do not need です or だ for the sentence to be grammatical.

You could say:

• 差し色が強いです。

if you want a more polite version.

Because 強い is an い-adjective.

With い-adjectives, you do not add だ in plain form:

• 高い。 = It is expensive/high.
• 強い。 = It is strong.

Adding だ after an い-adjective is incorrect in standard Japanese:

• ✘ 強いだ

If you want politeness, use:

• 強いです

Yes, but it has a different nuance.

• 差し色が強い = focuses on the fact that the accent color is strong
• 差し色は強い = sets the accent color as the topic, often with some contrast

For example, は might suggest:

• as for the accent color, it’s strong
• the accent color is strong, though maybe other parts are not
• compared with something else, the accent color stands out

If you are simply describing what stands out in the design, が is very natural.

Yes, possibly. Japanese often leaves out context that is obvious.

Depending on the situation, the full idea might be something like:

• この服は差し色が強い。
  The accent color in these clothes is strong.
• このデザインは差し色が強い。
  This design has a strong accent color.
• この部屋は差し色が強い。
  This room uses a strong accent color.

So the sentence by itself is natural, especially in conversation, reviews, fashion talk, or design comments.

Usually it is describing the visual impact of the accent color.

That can include:

• the color is very vivid
• the contrast is large
• the accent draws a lot of attention
• the use of the accent feels bold

So it is not only about the technical color value. It is often about the impression the accent color creates in the whole look.

Yes. Japanese speakers may choose different expressions depending on nuance.

For example:

• 差し色が目立つ。
  The accent color stands out.
• 差し色が効いている。
  The accent color is working well / is effective.
• 差し色が鮮やかだ。
  The accent color is vivid.
• 差し色が強すぎる。
  The accent color is too strong.

So 差し色が強い is natural, but it is one of several possible ways to describe a bold accent color.